# Intermittent Rear Brake Light / Tail Light Problem Ongoing



## davidf1 (Jun 10, 2013)

Hi all,last year I did the rear brake light fix by earthing,but recently,within the last two weeks,the rear brake light failure sign has come up on the dash display,but it seems very intermittent.Sometimes doesn't come on at all.I have checked the wire and both connections on the earthing fix.
The rear brake light is working,and not dimmed down.
Does anyone have any ideas what I can do to fix this issue

Thanks all


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## SwissJetPilot (Apr 27, 2014)

Couple of questions -

1. Did you do the earth retrofit for one or both rear lights?

2. Did you use the external ground point recommended in the video or the ones inside the trunk area?


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## davidf1 (Jun 10, 2013)

I did it for the one side only,it is the right rear brake light gone that keeps coming up.I earthed underneath the car.


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## davidf1 (Jun 10, 2013)

I have taken the rear light off and cleaned the connection block and pins with emery cloth.And put it all back together.
Hopefully will know later tonight when I go out if it's solved the problem.Cant say there was much of an issue with the pins or block.I know the pin that goes,but it wasn't bad,not dirty or chared.
if anyone has any suggestions,please let me know.
A new right rear bulb holder is around £50 from Audi.
Can't you get them anywhere else if I need to get one,seems a lot for not a lot.


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## SwissJetPilot (Apr 27, 2014)

Key points to consider when doing this -

• Do this for both left and right tail lights since the ground wires are independent of each other.
• Don't use the external ground points as they are prone to corrosion. There are two easy to access ground points inside the trunk.
• Cleaning or replacing the terminal and/or connector won't really solve the problem due to the ground plane design defect described below.
• While you have the tail light assembly disassembled, go ahead and replace all the bulbs; (x2) P21W and (x3) W16W.

*UPDATE* -

The design of the tail light earth/ground plane consists of two separate earth/ground planes which are staked one on top of the other at the connector junction. As shown below, the upper plane (blue) is for the two P21W bulbs and the lower plane (red) is for the three W16W bulbs. The point where the upper and lower planes are staked together seems to be where all the problems are arising as high resistance can develop between the two planes resulting in a burnt pin.

To resolve this, it will be necessary to make a "secondary" ground wire across the upper and lower earth/ground planes. This can be done by either soldering a jumper across these two planes, or making a jumper with ring terminals on each end and adding a contact point for the upper ground plane with a pan head screw.

More on how to do this *here*.

If you want to replace the connector for cosmetic reasons, here's a post on depinning the OEM and replacing it with a new one. Not difficult at all even using a cheap de-pinning tool off Amazon.

More on how to do this *here*.










*Non-OEM Earth/Ground Wire Installation - *

The extra ground wire should be Ø 2.5mm / 14AWG. There are two very good ground points inside the trunk area; one on the left side (shown below in a Roadster) near the location for the Bose Amp, and another in about the same spot on the right side near the battery. Run the new ground wires through the grommet to these points as it will ensure a better connection that won't corrode later on.

Any good automotive electrical shop or car stereo shop should be able to sell you a couple of meters of 2.5-diameter ground wire. NOTE - Brown is the typical VAG color for ground (earth) I just happened to be near a Renault repair shop and they gave me a length of yellow/green for free. I also recommend the automotive cloth electrical tape as it holds better than the plastic electrical tape. And while you have the assembly taken apart, it's a good idea to replace all the bulbs so you don't have to worry about them in the future.

1.) Disassembly the light assembly and drill a hole through the grey plastic housing, close to the ground trace.
2.) Insert a SST pan-head bolt through the hole, ensure a good contact with the screw head to the ground trace.
3.) Cut a piece of 2.5mm diameter ground wire aprox. 6"- long.
4.) Connect a ring terminal to one end of the ground wire and a male bullet (or spade) connector to the other.
5.) Place the ring terminal onto the screw (between the two washers) and secure with a nylock nut.

Re-assemble the tail light assembly, it's now finished. Repeat for the other one.

6.) Cut a 1-meter piece of ground wire and route it through the tail light grommet (easier from outside to inside).
7.) Route to the closest existing chassis ground-lug and cut to proper length.
8.) Attach a ring connector to the one end and a female bullet (or spade) to the other end.
9.) Connect the ring connector to the chassis ground lug.
10.) Connect the two bullet connectors and re-install the tail light assembly.

Repeat for the other side and you're done.

*Hardware:*
• 2-3 meters of automotive Ø 2.5mm (14 AWG) ground wire (Brown is the standard color for VAG vehicles)
• Ring connector (x4)
• Male bullet or spade connectors (x2)
• Female bullet or spade connectors (x2)
• SST pan-head bolt (x2), washers (x4) and nyloc nut (x2)
• Cloth automotive electrical tape
• Tail light bulbs: P21W (x2) and W16W (x3)


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## davidf1 (Jun 10, 2013)

How do you get the wire through the Oem grommet?


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## SwissJetPilot (Apr 27, 2014)

First, you'll need to pull the trunk side and rear panels and trunk tool Styrofoam inserts to get access, but that's pretty straight forward.

Easiest way is to first remove the OEM cloth tape from the grommet and then run the new ground wire through the grommet from the outside, pushing it into the trunk. It's a bit tricky, but be patient and you can get it through. The heavier gauge wire (2.5 mm dia.) is stiff enough it won't fold or bend. Just blunt-cut the end so the wire strands don't catch or snag the rubber.

Once through the grommet, pull it through from inside the trunk. Crimp a ring connector to the end and connect it to the ground point and arrange the wire where you want it. On the other end (where it come out at the light assembly) give yourself enough length to add the connector that's going to connect to the light assembly ground. If you have too much slack in the trunk, just pull it through from the outside. It doesn't need to be too long, (about half the length of the OEM wire/plug) since the longer ground wire from the light assembly should suffice.

If you have some handy, you can wrap a new piece of cloth tape around the wires and grommet to replace the one you removed. Once you do the first one, the other one will be much easier.

Not all that difficult, and IMHO worth the time and effort.


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## davidf1 (Jun 10, 2013)

That's great,one other thing though,how does the side panels come off,as I don't want to break anything.


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## brittan (May 18, 2007)

No need to remove the boot side panels, just the boot floor and the polystyrene tool holder parts. Pop out the grommet into the light unit recess. Crimp or solder the ring fitting onto the end of the wire and poke it through the body work hole so that it appears at the bottom of the boot panel. Fit it to the earth point.

Now poke the wire through the grommet - wetting the wire makes this easier. Your head is fitted with a handy wetting device. 
Now fit the external bullet or spade connector onto the wire.


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## SwissJetPilot (Apr 27, 2014)

Okay...looks like Brittan beat me to it! 

I believe the Roadster trunk panels are much easier to remove than the Coupe since we don't have the tie-down points to deal with. There are a number of clips that hold them in place, but once you get your hand behind them, they pull away quite easily. Study the workshop images and it should be pretty straight forward where things are as you will need to remove the tie down points (both sides) and the trunk light (right side). Just look around and you should be able to see what has to be removed before you can pull them - should you choose to do so.

As noted below, the styrofoam pieces are dove-tailed together, so remove the right one first and then the left one.
































.


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## davidf1 (Jun 10, 2013)

Where would I get the earthing cable from?


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## SwissJetPilot (Apr 27, 2014)

Any good automotive electrical shop or car sterio shop should be able to sell you a couple of meters of 2.5-diameter grond wire. Brown is the typical German color, I just happened to have yellow-green handy.

*NOTE* - Do not use solid (household or industrial) wire for the earth wire. Automotive wiring is always multi-strand to allow for flex and vibration.

https://www.ttforum.co.uk/forum/viewtop ... &t=1768698

1.) Disassembly the light assembly and drill a hole through the grey plastic housing, close to the ground trace. 
2.) Insert a SST pan-head bolt through the hole, ensure a good contact with the screw head to the ground trace. 
3.) Cut a piece of 2.5mm diameter ground wire (Audi cars use brown, but any color works) aprox. 6"- long. 
4.) Connect a ring terminal to one end of the ground wire and a male bullet (or spade) connector to the other. 
5.) Place the ring terminal onto the screw (between the two washers) and secure with a nylock nut.

Re-assemble the tail light assembly, it's now finished. Repeat for the other one.

6.) Cut a 1-meter piece of ground wire and route it through the tail light grommet (easier from outside to inside). 
7.) Route to the closest existing chassis ground-lug and cut to proper length.
8.) Attach a ring connector to the one end and a female bullet (or spade) to the other end. 
9.) Connect the ring connector to the chassis ground lug.
10.) Connect the two bullet connectors and re-install the tail light assembly.

Repeat for the other side and you're done.

Hardware: 
2-3 meters of 2.5mm diameter ground wire (wire strand, not solid)
Ring connector (x4)
Male bullet or spade connectors (x2) 
Female bullet or spade connectors (x2)
SST pan-head bolt (x2), washers (x4) and nyloc nut (x2)


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## tttony (Dec 21, 2014)

Brown is the correct colour wire to use for any earth (ground) connections on our cars.

In the UK green/yellow cable is only ever correctly used for the safety earth connections on mains (240v AC) supplies.


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## AndreiV93 (Mar 29, 2017)

I've actually just done this mod last Saturday using SJP's perfect write up  (Thanks SwissJetPilot!!!)

Like he said, using the interior ground point is better as they stay clean and dry. I was expecting a bit of a struggle to get the wire through the grommet, but it was much easier than I thought.

The trunk panels are very easy to remove, just pull on them gently. Just make sure you don't lose the small clips if they slide out.

Cable wise, I bought mine from eBay. I went to the Motorist Discount Centre and asked for a 2.5mm earth cable and they said they rate their cables in amps and he didn't know which one was the 2.5mm one :lol: so I decided to get it from eBay to make sure I got the right one; and it's brown  : (https://www.ebay.co.uk/itm/Single-Core- ... -5yXXjaRxg)


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## SwissJetPilot (Apr 27, 2014)

At the time I bought the wire for this project, I was actually on holiday in France and there was a local automotive electroincs shop in town. When I asked for a piece of 2.5 mm ground wire, he said he was all out of the brown which was typically used on German cars. But he did have the yellow-green which was for Renault. I told him my Audi TT was color blind so it wouldn't matter. He just laughted and sold me a 3-meter length. It's worked fine ever since.


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## davidf1 (Jun 10, 2013)

I will go through the grommet this time to earth in the boot,but why is the fault now happening again after around 6 months,I have cleaned and emery clothed both connections.And the bulb is good,and it's not duller in power.seems very intermittent


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## brittan (May 18, 2007)

davidf1 said:


> I will go through the grommet this time to earth in the boot,but why is the fault now happening again after around 6 months,I have cleaned and emery clothed both connections.And the bulb is good,and it's not duller in power.seems very intermittent


Have you tried changing the bulb even though it appears good?


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## brittan (May 18, 2007)

brittan said:


> davidf1 said:
> 
> 
> > I will go through the grommet this time to earth in the boot,but why is the fault now happening again after around 6 months,I have cleaned and emery clothed both connections.And the bulb is good,and it's not duller in power.seems very intermittent
> ...


See the post by TT-driver here: viewtopic.php?f=19&t=264435&start=150


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## davidf1 (Jun 10, 2013)

Why even though I have checked the cable and cleaned all connections is the fault still popping up every so often,what could it be?


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## TT-driver (Sep 14, 2010)

At start-up of the car, the central electronics perform a quick resistance check on various light circuits. If any or the resistance paths is out of specifications, the system logs a fault and switches off the circuit in order to protect itself.

So if an error pops up, the resistance is either too high or too low. Too low would indicate bulbs with too many Watts or a shortcut even. Too low would indicate additional resistance due to oxidation, or bulbs with too few Watts (like with LEDs)

- So check your bulbs, are they the correct ones?
- check the bulb fittings for oxidation
- check the pins in the socket and the wiring loom for damage.

In order to perform a proper earthing check you'll need a voltage meter. Measure the voltage from the minus on the bulb to the minus of the battery while the lights are on. Only when you have proper earthing the voltage between them is zero. If there is a voltage then there is resistance. With zero I mean 0.0 Volts. Not 0.3V or what ever. Really 0.0.

On the brake lights also do check the third brake light. If too many LEDs are broken, that perhaps may trigger an error too.


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## SwissJetPilot (Apr 27, 2014)

Even a small amount of corrosion can lead to a higher than normal resistance and trigger a fault. Mine was doing that very same thing. I even took a piece of 220-emery and with a toothpick, got it inside the contacts in an attempt to clean them up. But a few weeks later, the problem still persisted. Funny thing with electronics, it takes very little corrosion to create a great deal of resistance and mess up the signal. Ever since I did the retrofit ground wire, the problem has never returned because the ground signal is no longer going through the OEM ground wire in the plug.


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## davidf1 (Jun 10, 2013)

Would anyone be interested in doing the job for me?


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## davidf1 (Jun 10, 2013)

How do I get the boot side panel off,the side with the light on?


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## TT-driver (Sep 14, 2010)

You don't need to... there's a service opening in the side panel that allows access to the screw that holds the unit. The screwdriver handle is your tool to loosen that screw. Push the light unit sideways gently. Pull the unit about 1 cm out at the sharp corner where the bumper, the wing and the light meet. Once it pops loose there, gently pull out the unit rearwards.


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## davidf1 (Jun 10, 2013)

Brilliant,I have the cable through now,do I connect it to the earth where the battery is earthed on the car,pictures if pos.


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## davidf1 (Jun 10, 2013)

Sorry I mean where I see two other brown cables going to a earthing point


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## davidf1 (Jun 10, 2013)

Right finally got it done on the drivers side rear.looks a good job especially with the recommended earth cable 2.5.
So I went to the shops,parked up,and the blessed brake light came up again on the dash.What could it be.
Could it be the other passenger side that's at fault.or something else.


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## davidf1 (Jun 10, 2013)

Should I change the bulbs,even though they all light up.As my partner has checked.The pins are all clean,and the connector block.what could it be?


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## tttony (Dec 21, 2014)

The extra earth cable should always be added to both rear light units.


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## davidf1 (Jun 10, 2013)

Yes I understand that,is that why I am still getting a light failure sign


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## TT-driver (Sep 14, 2010)

On mine it tell exactly which side is wrong.

From where to where is your additional earth wire running?


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## davidf1 (Jun 10, 2013)

The earth is going from the earth point by the battery to the back of the light as per various videos I have seen.drilled through light,washer both sides so is touching the metal and bolted with a connector.It was fine for at least 4 months.
I have now changed it to 2.5 mm cable.not one strand.bullet connector.
It isn't telling me now which brake light it is,just the symbol comes up with a cross across it.


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## TT-driver (Sep 14, 2010)

Did you replace all bulbs, just to be on the safe side? If so, which bulbs did you use?

Mine tells in text what's wrong before showing the yellow bulb warning.


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## mjw123 (Jul 20, 2017)

Guys,

I've fallen fould of this and found one of the connector pins so badly corroded it broke off.

Is there anything i can do here ?



Can a local repair be achieved to avoid replacing the whole unit ?

tia,
Mike.


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## davidf1 (Jun 10, 2013)

I havnt replaced any of the bulbs yet,should I do that,or earth the other side first?


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## brittan (May 18, 2007)

mjw123 said:


> Guys,
> 
> I've fallen fould of this and found one of the connector pins so badly corroded it broke off.
> 
> ...


You can buy just the bulb holder part of the light unit. Also the plastic plug part on the end of the wiring harness and a repair wire for the burnt pin.


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## davidf1 (Jun 10, 2013)

There is nothing wrong with the pins or plug.should I get new bulbs,or do the earth on the other side first?


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## TT-driver (Sep 14, 2010)

From that picture it's clear that the original earth pin is toast. Check the other side too. It might be just as bad. In that case, add earth wire on the other side too. Sooner or later you'll have to do that anyway.

Clean the bulb holder pins as much as possible and verify that all the other pins are still OK. If they aren't, it's time for another bulb holder. Also verify that the loose earth pin doesn't short circuit with any of the other pins. If that is the case -> new bulb holder.


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## davidf1 (Jun 10, 2013)

That picture is someone else's post


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## TT-driver (Sep 14, 2010)

OK... still check the other side first then.


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## Zombie (Jul 8, 2015)

mjw123 said:


> Guys,
> 
> I've fallen fould of this and found one of the connector pins so badly corroded it broke off.
> 
> ...


Hi, yes the Earth bypass mod will fix that.


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## Zombie (Jul 8, 2015)

After doing this Modification if the earth is good, then a faulty bulb or holder would be next on the list to change /check

As said normally in the dis just before the bulb symbol stay on it says what's at fault(for a couple of seconds )


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## davidf1 (Jun 10, 2013)

Ok yesterday I did the earth on the passenger side.But this morning when parking at work,the display again showed bulb with a cross through it.I just don't know what to do now.I could change the bulbs for new ones,but they seem to be working.
What possibly could it be?


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## AndreiV93 (Mar 29, 2017)

Guess the next step is to change the bulbs;

Like TT-driver says in this post: viewtopic.php?f=19&t=264435&start=150
"Then I opened up the rear light unit. Here I found that the glass wedge bulbs (W16W) were showing signs of oxidation on the small wires that connect them to the bulb holder. I replaced the bulbs, that were still the original bulbs, so close to 12 years old. And the problem is gone!"


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## davidf1 (Jun 10, 2013)

Ok I will change the w16w bulbs tomorrow,what about the others?


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## AndreiV93 (Mar 29, 2017)

Depends on the age or the car I guess, but if they're still the original bulbs, I would probably change all of them for that piece of mind


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## davidf1 (Jun 10, 2013)

What's the best make of bulb to replace these.


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## SwissJetPilot (Apr 27, 2014)

@ *DavidF1* - Stick with major brands; Osram, Sylvania, GE, etc. and you should be fine. If you car is over 10-years old, or if you see "silvering" inside the bulbs, it's probably a good idea to just replace them all at one go so you're good for another 10-years.


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## davidf1 (Jun 10, 2013)

If it's not the bulbs,what could it be?


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## TT-driver (Sep 14, 2010)

Damaged wiring? A bulb at the front? The third brake light? Licence plate light?

Perhaps visit a dealer to get a detailed error log from the car.


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## davidf1 (Jun 10, 2013)

Could it be the light cluster fitting on the drivers side.Even though the pins all look ok.The third brake light would be a pain to get to,all leds light up and none are not working,and I see no water ingress.
I am really hoping that by changing all the bulbs in the drivers side rear,will sort the problem out.
If there is anyone that can help,I really would appreciate it,the cars mot is in 3 weeks.


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## SwissJetPilot (Apr 27, 2014)

@ *DavidF1* - When my rear lights were failing (before I did the earth retrofit) the left rear light would come on, but then after about 5-10 seconds, it would fade out and then give me the error on the DIS (Drivers Information System).

Given the issue with the resistance in the rear plug (the burned pin shown previously) it takes a few seconds after turning on the light in order to generate the appropriate resistance for the car to recognize the fault. When the fault it detected, the car will automatically shut off power to the light even if it's a good bulb. Which is what's happening with the rears due to a bad ground pin, and not a bad light bulb.

Try cycling through each the positions of the light switch and have someone watch each bulb. It may come on and then go out if the connector is faulty as is the case for the rears. Give every light a chance to light up and see if it remains illuminated by leaving it on for 30-60 seconds and then check to see if you get the error.

Here's a list of bulbs for the TT -

https://www.ttforum.co.uk/forum/viewtop ... t#p8342042

Be aware this list may not be 100% accurate depending on your year and model. The best way to verify what you have is to simply remove it and check each one so you know exactly what your car was fitted with.


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## davidf1 (Jun 10, 2013)

Ok went to work today,and the light came on,said right brake light,so after work went to halfords and got all new bulbs for the drivers side rear light,and have put them in,checked all fittings,and plug and pins and earth,all good,so I am hoping it has solved it.will see tomorrow.


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## nhs99v (Jul 18, 2017)

I'd love to know how this post is 4 pages long.

There is loads of 'previous' on the subject in the knowledge base and 4 pages in, you finally actaully spend some mnoney and buy new bulbs which would probaly have set you back a fiver at the most..

Contributes nothing to the knowledge base this post and should be removed.

Also, not once have you actually thanked anyone who has gone out of their way to answer the million questions you've posted.


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## davidf1 (Jun 10, 2013)

Seems the problem has gone away since changing for all new bulbs.
Thankyou for everyone's help.It is appreciated.
As much advice as possible is allways better.


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## SwissJetPilot (Apr 27, 2014)

Excellent! [smiley=cheers.gif]


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## liam (Feb 8, 2010)

It's been a while but I'm back bought a MK2 Audi TT black edition, with 40k recently I have seen this strange light issue where it's bright and dims if I keep pressing the unlock button it improves the brightness and if I unlock boot it lights up all the way.. Is this the same issue with a dodgy earth?

If so is there anyone located in Cheshire who could help me with this mod?


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## PAF (Apr 22, 2012)

Great post ,
Our 2013 Mk2 TTS Roadster just suddenly lost all three bulbs on the right side new it had to be an earth fault
But this with clear and concise instructions solved the problem easily

Thanks


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## mjh2222 (Feb 2, 2019)

I have exactly this issue right now with my rear left light/brake light, with the warning that the light is out coming up on the dash and coming up each time I press the brakes telling me the rear left brake light is out.

Could someone please explain how to fix this to a person who does not even know what earthing is lol

Is this fixable for someone who does not know about electrics?


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## Hoggy (May 8, 2002)

mjh2222 said:


> I have exactly this issue right now with my rear left light/brake light, with the warning that the light is out coming up on the dash and coming up each time I press the brakes telling me the rear left brake light is out.
> 
> Could someone please explain how to fix this to a person who does not even know what earthing is lol
> 
> Is this fixable for someone who does not know about electrics?


Hi, You have been given one link & here is another & yes this very common prob is easily DIY fixable
https://www.ttforum.co.uk/forum/viewtop ... 3&t=332559
Hoggy


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## mjh2222 (Feb 2, 2019)

Thank you, should have all the info I need now.


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## SwissJetPilot (Apr 27, 2014)

Be aware that both tail lights will need their own non-OEM ground (earth) wire. Once you have the foam tool trays out of the way, you will see the two common ground lugs located in rear-most corners.

When you remove the foam tool trays, remove the right one first (battery side) as they are dove-tailed together.

*Any idea if the factory grounding points are any good?*
https://www.ttforum.co.uk/forum/viewtop ... &t=2006929


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## shajar (May 19, 2021)

Great write up 'SJP' thumbs up!
Had this nailed on the weekend fixing the left rear brake light out issue we were seeing, the right rear was about to go to, so did both a the same time, I spliced the OEM ground wire into the same circuit rather than bypass it completely in-case of any ECU circuit faults arising.
Thanks again for this information and well detailed write up, invaluable info.


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## TT'sRevenge (Feb 28, 2021)

I took out my lights to do this today and also to start on some stereo stuff--have most of the trunk apart. I had noticed last year one of the two lights was visually dimmer than the other (can't remember which), so figured I'd have to take care of this.

I've been over/through nearly everything on this car and everything was bone stock as I bought it but found the first "odd moment of prior repairs" when I pulled those tail lamps...the right side one already had some kind of repair done:









The right side one was as factory, so no repair was done there but I _do_ have the burned up ground pin as shown in the other pictures.

I dunno what happened to the right one but I'm guessing the same issue caused it to cut out and this was how whoever repaired it...decided to repair it, not understanding the issue is rooted in the grounding of the interior. Anyway guess I will just perform the extra ground on both sides, seems easy enough.


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## SwissJetPilot (Apr 27, 2014)

Geeze...and they didn't even bother to go with OEM wiring...


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## TT'sRevenge (Feb 28, 2021)

SwissJetPilot said:


> Geeze...and they didn't even bother to go with OEM wiring...


Yeah it doesn't really look like the prettiest repair but seems good and functional. I mean the light was working fine and I can't even remember which side was the "dimmer" one--it may well have been the side without the repair. The repaired side the connector was replaced with a new one... As the lamps ground terminal on this side was even worse, I'm guessing what happened here was the connector got badly melted and led to the inop light and the repair seen. 

I think whomever worked on it thought the corrosion/problem was caused by water intrusion, hence the silicone or whatever jammed into the other side lol. I don't think they were familiar with the fact that it's really an inadequate ground that's the culprit. I'm actually pretty surprised Audi would do something like that--one ground wire/pin for everything in the lamp lol 🤦‍♂️

Anyway I finished up the mod/fix on both sides, did pretty much exactly as indicated here, was pretty easy to do. I sanded the ground terminal in the connector as best I could as well, sprayed some silicone spray after. Treated the seal/gasket with some Dow 111. 

The stainless hardware I had on hand was just hex head, not too big so I used washers for better contact. Couldn't find any Nylocks so I just used the SS nuts I had, hopefully they don't go anywhere lol. Also seems there's a coating on those buss bar things, so sanded it to get better contact. I think I'm good to not have any issues come up in the future  Polished up the lights with Plast-X while I had them out too.

On another note I noticed there's a little rubber bumper that goes on the top inside corner, and it's missing on the side that was repaired--guessing it came off and was not noticed by the mechanic. I'll have to look up the part# for that, see if I can get a replacement. Also does anyone know if the rubber seal thing on the inside of the trunk goes over the body seam there or under? I didn't really pay attention when I removed it and it seems like it can go either way. Not really a big deal I don't think


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## Wolvez (Jun 22, 2018)

TT'sRevenge said:


> I think whomever worked on it thought the corrosion/problem was caused by water intrusion, hence the silicone or whatever jammed into the other side lol. I don't think they were familiar with the fact that it's really an inadequate ground that's the culprit. I'm actually pretty surprised Audi would do something like that--one ground wire/pin for everything in the lamp lol 🤦‍♂️


Nope, look at the tail light terminal and you'll see small gap allowing moisture to enter. Both of my tail lights are fine. I used grease to seal the gap. But both of my headlights bulb holders are partially melted. The wire insulation completely failed. All the ground on this car are designed to fail because they used different types of metal. Also look at the big possitive wires going to the fuse box on the engine bay. Most of them don't even have heatshrink just like the huge + cables on the battery.
A maintenance free DC electrical connection will use same type of metal on the terminal, stud, nut and bolts to prevent corrosion.


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## Henrik964 (4 mo ago)

Do I have this on my car? Ohhh yes.


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## SwissJetPilot (Apr 27, 2014)

So despite having done the non-OEM Earth Ground fix, for whatever reason, my left tail light started acting weird since it`s suddenly half the intensity of the right side. Although quite dim, the P21W lights are definitely on, but there's no DIS warning or a DTC being reported. I suspect the ground plane or possibly the connector itself.

The left side indicator and brake lights work properly. I've replace the two P21W bulbs on both the left and right lights so I know they're new. Depending on how things look once I have removed and inspected it, I may follow the recommendation from this earlier *thread* by *tomasfuk* post and solder the two ground planes together and see if that resolved the problem.

After arriving at work this morning at o'dark thirty, I had another look at the tail lights. With the lights turned on as usual, the right one looks normal, but the left one is still quite dim however the left indicator works normally. Just as I was about to take this photo, I noticed the left lights started going brighter and then dimmer, then brighter and dimmer.

Weird.


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## SwissJetPilot (Apr 27, 2014)

I pulled the left tail light assembly out when I got home. The connector is even more burnt that when I originally tackled this problem and installed the non-OEM earth/ground wires on both left and right tail light assemblies .

As soon as I got home and went to remove the left tail light I could feel the area at the connector was quite warm. Not hot, but much warmer than I expected. Once I had it out of the car and onto the work bench, there was an obvious burnt smell too.

I put a meter on both ground planes and had almost no connectivity between the lower plane (three smaller W16W bulbs) and the upper plane (two P21W bulbs) so my hunch was right - the problem is due to poor contact of the two metal ground planes.

I soldered a length of wire across both planes and got full connectivity this time, so hopefully this sorts it. Unfortunately my soldering iron can't put enough heat into the heavy ground plane, so it was a challenge not getting a cold joint. I may have to do this at work and put some serious heat to it.

Not much I can do about the condition of the male connectors in the tail light assembly, but I'm seriously debating replacing the female connector and re-pinning the whole thing given how badly this has burned. Any advice from anyone who has re-pinned one of these?

*De-Pinning and Replacing the Connector - *

I've started this *post* to discuss de-pinning and pinning connectors and terminal replacement. Actually it`s pretty simple and doesn`t require an expensive de-pinning tool.


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## TT'sRevenge (Feb 28, 2021)

Man these tail lights are a damn pain! Audi really botched the job on these eh? So even if we did the 2nd ground, there's potential for more problems down the road! Just greaattt 😕

Hopefully you get yours working properly SJP. Also I wanna say perhaps the right side in your pic is too _bright_? Or perhaps that's just because of the glare in the picture? I don't think mine are as bright as your right or as dim as your left, it's more like somewhere in between I'd say!


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## SwissJetPilot (Apr 27, 2014)

Yeah, tell me about it! 

It's the glare. My cellphone camera is really light sensitive so they both lights look brighter than they really are. I was going to take a picture during the day, unfortunately, the left tail light is so dim as to be nearly impossible to see illuminated in daylight.

I'll test this repair in the morning and if it works, then I will do the right one too just so I don't have to worry about it later on. It's not a difficult job, but no one should have had to do this in the first place!

Next challenge will be the ground wire terminal and connector repair. Link *here*.


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## MT-V6 (Jan 11, 2015)

Hmm didn't realise the inside ground tracks were poorly joined also. I guess I'll have to take mine out for a second round of preventive maintenance...


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## MT-V6 (Jan 11, 2015)

For the join under the bulb, on the bottom right of that photo, could you just crimp on a ring terminal and put it on your other ground mod bolt head?


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## SwissJetPilot (Apr 27, 2014)

I would think you could go that way too.

It might be just as easy to drill another hole through the plastic case next to the upper ground plane and insert a pan-head screw at that location. Then connect the ground wire across the upper and lower ground planes with ring terminals on both screws. I may go this route with the right tail light as an example for using a wire and ring terminals since soldering may not be an option for everyone.

Which ever option you use to connect the two ground planes, keep in mind the screws, terminals and internal ground wire must be positioned to avoid any interference when the two halves of the tail light assembly are put back together.


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## SwissJetPilot (Apr 27, 2014)

If soldering isn't a option, you can use an 18cm-long jumper wire with two 1.25-6/22-16/D8 ring terminals on each end. This will require a hole for the bolt or screw close enough to the upper ground plane to ensure a good contact for the ring terminal. Then connect the other end to the primary non-OEM ground/earth connection. Nylock nut to secure it in place and that's pretty much it.

I also included a picture of the right side connector which is undamaged is as it should be. Based on the reports of this failure, it seems to be more frequent with the left tail light assembly which would make me believe it was a manufacturing defect where the upper and lower ground planes were not staked properly.


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## TT'sRevenge (Feb 28, 2021)

MT-V6 said:


> Hmm didn't realise the inside ground tracks were poorly joined also. I guess I'll have to take mine out for a second round of preventive maintenance...


Hmm maybe if we keep these cars another 10 years, we'll be having to run _wires_ to all the bulbs, lol. Probably what Audi should have done in the first place instead of this bus bar thing.


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## SwissJetPilot (Apr 27, 2014)

My new tail light connectors and de-pinning tools arrived today. Guess what I will be doing this weekend! 

I'll be making the swap and documenting it over on this post -








De-pinning and Replacing Damaged Connectors - Tail Light...


My tail light connector ground pin is toast and I'm thinking about buying a connector off eBay, de-pinning my original connector and replacing it. Does anyone have experience doing this and can provide some advice and/or recommendations regarding pinning/de-pinning tools...? Also, how to...




www.ttforum.co.uk


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## Henrik964 (4 mo ago)

OK after reading through the complete thread I have one question before I start. (experience from a much older car with earth problems on the headlight) What fuses does it blow if I fail to get solid ground? I cant figure out from the fuse table? OR does it hit a relay? Dont wont to end up with no brake lights after the fix....


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## Wolvez (Jun 22, 2018)

Henrik964 said:


> OK after reading through the complete thread I have one question before I start. (experience from a much older car with earth problems on the headlight) What fuses does it blow if I fail to get solid ground? I cant figure out from the fuse table? OR does it hit a relay? Dont wont to end up with no brake lights after the fix....


The lights don't have fuse. All the lights except the rear interior and turn signal at the side mirror are directly connected to the central electric module. *The LEFT tail light, 3rd brake light & spoiler ground is located at the c pillar. #7 or #8 **NOT #6*. The right tail light ground is #5. On a direct current when you connect 2 dissimilar metal together corrosion will always occur if the connection is not sealed. Use brass wire brush to clean copper terminal. Use fine sandpaper for terminal plated with tin.


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## Wolvez (Jun 22, 2018)

If the ground terminal is already burned you need to replace the crimp terminal. If the ground terminal is still ok, not yet burned or melted use a bulb grease to seal the gap and prevent moisture getting inside the connector. Make sure to also clean the bulb and the terminal on the bulb holder. Apply small amount of bulb grease at the embossed dot of the bulb to prevent corrosion. If you have a terminal release tool, remove the terminal then apply small amount of grease on the wire seal and connector seal. 










Don't seal the vent hole, just pointing it out just in case your not aware that the tail light housing is not sealed.


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## Henrik964 (4 mo ago)

OK, NO fuses on the rear?? 
This is a new thing to me. SO if I short corcuit the ground I hit the centreal electric module OR all the lights go?? Has anyone experience of this? Thanks for inout! 



Wolvez said:


> The lights don't have fuse. All the lights except the rear interior and turn signal at the side mirror are directly connected to the central electric module. *The LEFT tail light, 3rd brake light & spoiler ground is located at the c pillar. #7 or #8 **NOT #6*. The right tail light ground is #5. On a direct current when you connect 2 dissimilar metal together corrosion will always occur if the connection is not sealed. Use brass wire brush to clean copper terminal. Use fine sandpaper for terminal plated with tin.
> 
> View attachment 494468
> 
> ...


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## MT-V6 (Jan 11, 2015)

It's fused via the control module as mentioned, would be far too many fuses if everything had its own. Power goes via fuses to the module, then to the various lights


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## Henrik964 (4 mo ago)

So Its the control module fuse that goes if I connect the ground wrong?
It this fuse 15?
I have copper washers etc, the stuff needed to get it right..but im always careful, from earlier experience earth can be a tricky thing...


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## Wolvez (Jun 22, 2018)

Henrik964 said:


> So Its the control module fuse that goes if I connect the ground wrong?


Nope, NO FUSE. The CECM will act like nothing happened. For example, the headlight turn signal + is short to ground. Same error when no bulb installed. You will hear a beep then it will illuminate the bulb warning at the cluster & set DTC saying + is short to grounrld. As soon as the turn signal + wire stop touching or making contact to the ground, the bulb warning @ the dash will turn off. Turn signal will work like nothing happened. The CECM don't interrupt the power on the lighting circuit. Only the level motor circuit is interupted when fault is detected. It requires restarting the ignition switch.

The wire insulation on my left headlight completely failed. European vehicles with wiring inside the headlight are very notorious for failing wireinsulation. I prevented few wire insulations from failing on my right headlight using heatshrink.



Henrik964 said:


> I have copper washers etc, the stuff needed to get it right..


The washer should be aluminum not copper.


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## Henrik964 (4 mo ago)

OK that i did not know x 2!

Thank You Sir. Why not copper washers? I will start doing this!
Excellent input.


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## Wolvez (Jun 22, 2018)

Read this Aircraft Electrical System Bonding and Grounding Procedures

Nickel Zinc plating/coating is alternative to cadmium

Just in case your doing preventive maintenance on your headlight. To remove the electrical connect on the heqdlight see image below.


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