[tttony]

It's likely to be a poor internal earth within the light unit. See this thread:-

Another rear light failure mode.

I don't think that this has been covered here before. A couple of weeks ago my neighbour told me that my right tail and brake lights were not working. I had not had a bulb failure warning on the DIS. I carried out the additional earth wire modification years ago. I removed the light unit and...

www.ttforum.co.uk

 

[Jezzie]

Any advice to check the circuits etc please let me know. thanks

There are two separate strips of earth metal inside the liight unit that are joined together by melting a plastic peg (the same way that all of the metal strips are held down). If you search the forum you should find pictures showing how to solder across this poor earth joint.

 

[tttony]

Jezzie, that is the subject of the thread that I linked to.

I would strongly suggest that soldering is not the best option.

 

[Jezzie]

Jezzie, that is the subject of the thread that I linked to.
I would strongly suggest that soldering is not the best option.

Oops!

 

[fubar7]

Jezzie, I get the idea you're suggesting. I will connect them without soldering (just to see)

 

[SwissJetPilot]

@ Jezzie - Generally speaking, you do NOT want to solder automotive connections; crimp connections are sufficient if they're done correctly. However in this case, there is a possibility that the ground plane inside the tail light assembly may have a bad connection (e.g. corrosion, poor metal-to-metal contact, etc), thus the soldered connection to resolve this issue.

 

[E.L.Wisty]

Generally speaking, you do NOT want to solder automotive connections;

SJP that's interesting - and useful advice, thanks - is that because of the level of vibrations in an automotive environment?

 

[SwissJetPilot]

@ E.L.Wisty - Generally speaking, yes. NASA has a few points on the topic -

Inspectors

201 CRIMPED TERMINATIONS GENERAL REQUIREMENTS

 

[fubar7]

Problem solved!

Although I have been told never to replace a car part unless it's broken (especially on an German car), I have heard others on this forum suggesting after the rear light fix, to just go ahead and retrofit the non-affected passenger side as well. I think that is wrong advice. In addition to that, it is suggested to replace all the bulbs as well, even when they are not an issue I believe is also excessive. The problem comes down to isolating the fault in stages.

However, when I upgraded the corresponding unaffected passenger side (which was okay at the time) it created a problem concerning one of the tail/brake bulbs on that side. It turns out it WAS the bulb at fault but because of all the changes there was no way to figure that out as being the problem. So best advice is don't replace was isn't broken, and work methodically. Although the fault was not due to a blown bulb, it would light a 5W bulb, so not being an electrician, I was at a loss to figure out why it was doing this. I believe the upgraded side grounding strip (which was on the outside brake part) reduced voltage to the corresponding side and that was the issue. If anyone can figure out what went wrong, please post it.

I don't think anyone should be sent to the Tower of London over it but tears have been shed...

 

[FNChaos]

Problem solved!

snip--> However, when I upgraded the corresponding unaffected passenger side (which was okay at the time) it created a problem concerning one of the tail/brake bulbs on that side. It turns out it WAS the bulb at fault but because of all the changes there was no way to figure that out as being the problem.

Electrically speaking, an incandescent light bulb is a resistor.
Electrically speaking, a corroded / overheated / damaged connection is a resistor.

Your car checks for burnt out bulbs by comparing expected current flow through your lighting circuit with what is actually measured. A burnt-out bulb has infinite resistance and that change in resistance causes a change in current flow.

It is quite possible to have a bad / corroded connection that provides enough resistance to compensate for an open bulb. Fixing this connection would then exposure the underlining problem (defective bulb).

I have heard others on this forum suggesting after the rear light fix, to just go ahead and retrofit the non-affected passenger side as well. I think that is wrong advice.

Proactively addressing known failure points is good practice. If you wait for things to fail they will likely do so at the most inopportune moments.

 

[bigkevgarrickrfc]

Various topics appeared on this forum already regarding the rear light cluster packing up completely.
As we've seen in the other topics, it's mostly due to a corroded earth connector in the plug/socket.

In my case however the connectors were still reasonably clean and no signs of overheating. Hopefully I now have a solution to the problem as it appeared in my September 2006 TT.

First of all, I noticed that the resistance from plug to the car battery was 0.6 Ohm and not 0.0 Ohm as should be the case. The root cause appeared to be at the other end of the wire, in the boot corner of the car. I disconnected it, used a fine grid sand paper to clean the bolt, the 'O' connector and the body work. Reinstalled the connector and result: 0.0 Ohm now. No resistance any more from plug 'all the way' to the battery.

Next point of attention: the actual connection from plug onto the bulb holder. Two issues here:

1) the metal used as wire on the holder corrodes. This corrosion turns into electrical resistance. Current and resistance create heat. From there things just go pear shaped.

2) the actual connector for earth imho is too small really. When brake lights, indicator lights and reverse light are on all at the same time, we're looking at 2*21 + 2*16 + 1*16 Watts = 90 Watts, close to 7A. That is a serious current.

I think this is a bit of a design flaw and replacing the bulb holder will only help if Audi uses a more suitable metal for the current ones. I don't know if they do.

This week I thought hard of a solution that did not involve running off to Audi and that had to be mostly reversible just in case it wouldn't work out. I think I've got it now.

First I looked for a suitable point for creating an additional earth connector, without the need of drilling a hole in the body. Found it:

This is one of the 4 bolts holding the beam behind the rear bumper on to the bodywork. I connected a 50cm wire with a soldered O ring to it to this point. Applied some wax afterwards, protecting the bolt and connector from dirt and water.

Next I looked up a suitable place to drill a hole in the bulb holder plate:

I cleaned the 'wire' locally a bit (after taking the picture) and put a screw in with washers at both sides:

And the other side:

Now the mounting on the car. Used a wing nut so I can undo the additional connector (and the whole light unit for that matter) without the need for any other tools than those supplied with the car. Here you see the light unit turned upside down, with the additional earthing connector connected.

The location of the connector was chosen in such a way that the likely hood of it getting into contact with water is quite small. Still after making the connection, I applied again a bit of wax.

So that's it: an additional earth connector to the light unit. It's installed on the right hand side now. When comparing the units left and right, I can see that the intensity of the rear lights and the reverse lights is more stable with the indicator switched on than on the left hand side. A clear sign that on the left, the unit is still suffering from a poor earth connection. Hope this solution will prove itself for years to come. Took about an hour to install and a couple of hours of thinking. If it doesn't work, it's all reversible except for the 3mm hole in the bulb holder. But that holder would have to be replaced anyhow in case this fix doesn't work long term.

For the sake of completeness: this is the right hand side unit on a left hand drive car. When applying the same 'upgrade' to your own car, ensure that it's the correct 'wire' in the unit that you're connecting to earth. Otherwise you'll create a short circuit. And at all at own risk. Feedback is welcome.

Edit: restored the links of the pictures. Thanks to Brittan for copying them for the knowledge base
Edit2: restored the links once more. Pictures are now hosted by the forum itself

Hi I done everything in your post but the issue I'm having is when my side lights/dipped beam is on my rear indicators are 80% illuminated and when I indicate they brighten up to 100% all others work as normal.when I unlock the car the inner left bulb illuminates until car is locked it goes out.😵‍💫

 

[SwissJetPilot]

For whatever reason, my left tail light is still not functioning properly and is half the intensity of the right side. The lights are on, and there's no DIS warning or a DTC being reported. However it's very dim so I suspect of the ground plane or possibly the connector itself.

The left side indicator and brake lights work properly, so not quite sure what's going on. I've replace the two P21W bulbs on both the left and right lights so I know they're new. Guess I will be pulling the tail light assembly apart once the rain quits to see what's going on.

Depending on how things look, I may follow the recommendation from this earlier thread by tomasfuk post and solder the two internal ground planes together and see if that resolved the problem.

NOTE - this thread has been continued in this post

 

[Wolvez]

Both of my right brake light stop working last week. I assumed the ground terminal or the bulb failed but after inspection I found out both ground and bulb are OK. I sprayed conact cleaner and installed the bulb back but still not working. I swap the bulb with LED but still not working. I cleaned the terminal that makes contact with the bulb using brass wire brush and sand paper. It fixed the problem. I don't see any visible corrosion on the terminal.

 

[Henrik964]

OK did the ground project after a great guide. Right hand side, rear. All works, ground point to inner right side, Drilling point, hole for the screw and went through the OEM rubber stopper with the cable. All good. All works. No more beep and warning rear light out. Pics for documentation.