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:
![Image]()
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:
![Image]()
I cleaned the 'wire' locally a bit (after taking the picture) and put a screw in with washers at both sides:
![Image]()
And the other side:
![Image]()
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.
![Image]()
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
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
