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?

 

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.

 

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.

 

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.

And for anyone who doesn't have the skills for cutting/crimping wires, you can buy a ready made DIY kit from forum member Chrisj82.

eBay link 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)

"Burn" mark on the earth/ground pin inside the tail light assembly housing -

Hole drilled close to the ground plane from inside the assembly -

Large pan-head bolt provides full contact with the ground plane from inside the assembly -

Non OEM ground wire and ring terminal connected to the outside of the tail light assembly -

Location of chassis ground lug aft of the battery used for the right tail light -

Location of chassis ground lug used for the right tail light -

Non OEM ground wire can be worked through the existing grommet (left side shown) -

Bulbs used for the tail light assembly -

 

How do you get the wire through the Oem grommet?

 

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.

 

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

 

Take a look at the pictures and you can sort out where the panel clips are located. You can use a plastic pry-bar of just get your fingers behind the panel and give it a quick jerk. Try to get your fingers or pry-bar as close to the clips as possible.

Put a ring terminal on one end of the earth wire and connect it to the earth lug inside the boot. Pull out the grommet from outside where the light assembly fits in. Reach into the boot and fish the earth wire up through the opening left by the grommet.

Now poke the wire through the grommet - wetting the wire makes this easier. Your head is fitted with a handy wetting device.

Once the wire is through, fit the external bullet or spade connector onto the wire and re install the grommet.

 

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.

.

 

Where would I get the earthing cable from?

 

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)

 

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.

 

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)

 

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.

 

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

 

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?

 

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?

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

 

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?

 

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.

 

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.

 

Would anyone be interested in doing the job for me?

 

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

 

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.

 

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.

 

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