# Is the rear light fault a reoccurring problem?



## Ryan1749 (Aug 24, 2017)

I purchased an 09 plate TT from a garage 10 months ago, when I bought the car it had the common rear light fault on the passenger side so the garage agreed to fix it free of charge. Now the problem has occured again but this time on the right hand side of the car, obviously not under warranty anymore I will have to pay for it myself, but my question is has anyone ever had the issue fixed and then its happened again on the same bulb? Or are the parts supplied by dealers now improved to prevent the issue? Thanks in advance


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## Zombie (Jul 8, 2015)

No. Generally a burnt earth pin in the connector

This is what I did


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## Bobo2211 (Sep 27, 2015)

this issue is pretty common, mine had it too.Should do as Zombie suggested, add extra earth to the bulb holder


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## SwissJetPilot (Apr 27, 2014)

Before you jump on that repair band-wagon, check that it's not a front light that's out. Here's why...

I received a failed lamp warning for my rear light and sure enough the left rear was out. So I pulled the rear light assembly, cleaned the terminals and put it back. Switched on the lights, went to look and sure enough it was still out. Upon a second inspection of the bulb, I couldn't see anything broken, so I switched the two P21W blubs and sure enough the same position went out again - with a good blub!

Then I had my wife turn off the lights and then turn them back on again. They all came on, but after about 2-seconds, the rear light went out. Okay, so that was weird. So I checked the front lights and sure enough, the right outside marker light was out. I replaced it and the left rear light hasn't been a problem since.

So before you start drilling holes in your rear light assembly, double check all your bulbs. One of my DRL bulbs actually came apart (the bulb separated from the metal case) when I tried to get it out of the holder to check the filament. So it may just be these older bulbs are just wearing out (like old things do).

I'm now in the process of replacing all my exterior blubs (less the Xenon) since they're cheap and easy enough to do.

Also, don't trust your owners manual! Mine was obviously an early 2007 manual, and my TT is a later 2007, early 2008 since what the manual said I have and what is actually in the vehicle are completely different. My manual shows I don't have Xenon (and I do) and it also stated the outside marker was a bare bulb (without the metal case), which was also wrong!

Outside Maker.............H6W
Turn Indicator.............H21W
Daylight Running Light...P21W

.


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## TT-driver (Sep 14, 2010)

Hmmm.... my 2006 manual mentions the W5W bulb as a side marker for Halogen light units and H6W for Xenon light units. 
I guess if you paid Audi for Xenon, they installed a slightly brighter H6W bulb too.

But they are mentioned both. I do have Xenon on mine. Oh and don't forget: these H6W bulbs run hot. So don't touch them with your fingers. Grease from fingers may shorten their life, much like with the dipped beam bulbs.


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## SwissJetPilot (Apr 27, 2014)

There are two very nice ground points in the trunk area of the Roadster. I would guess if you pull the trunk liners and carpeting you'll find them in the coupe too. Can't even imagine using an external grounding point when these nice, clean and dry points are available. Noted in the picture are the two on the left side, the one closest to the tail light is the easiest to get to. There's another in about the same location on the right side, near the rear right corner of the battery that is also easy enough to access.

The only way this would be a ground-fault is if all the bulbs are not lighting up. The design of the grounding leads in the housing assembly is redundant so there's no way a single bulb can go out because of a bad ground. If one goes because of a bad ground, they all go.


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## tttony (Dec 21, 2014)

The answer to the original question is yes - probably. The underlying problem is that the earth contacts in the light unit and the mating plug are undersized. Installing a new earth wire that bypasses the problem area is a permanent solution.


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## brianmcc51 (Oct 4, 2014)

SwissJetPilot said:


> There are two very nice ground points in the trunk area of the Roadster. I would guess if you pull the trunk liners and carpeting you'll find them in the coupe too. Can't even imagine using an external grounding point when these nice, clean and dry points are available.
> 
> The only way this would be a ground-fault is if all the bulbs are not lighting up. The design of the grounding leads in the housing assembly is redundant so there's no way a single bulb can go out because of a bad ground. If one goes because of a bad ground, they all go.
> 
> ...


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## Zombie (Jul 8, 2015)

When I said this is what I did, I used the earths in the boot and not the external one used in the you tube link I supplied ( it was just the best example of what I did)
I used a post on here but all the photos have gone.

The error warning would come on I would check the lights sometimes they were on sometimes not, carried out the earth bypass mod a couple of years ago and never had the problem again.

As to drilling the holes it's just the bulb carriers that need drilling so you can easily return to stock if you wanted.


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## SwissJetPilot (Apr 27, 2014)

I would agree that the "burn" indications seen in the picture below is most likely a combination of two events happening at the same time; (1) an over current situation (all five lights operating simultaneously and pushing current through a single 18-gauge return ground) and (2) a dirty or corroded contact between the male-female ground pins in the connector creating additional resistance and a "hot spot" which is sufficient to melt the plastic.

If this is the case, then yes, the alternate ground solution does makes sense. But I'd use a larger 12-14 gauge (2.5mm)grounding wire and connect to the cleaner earth contacts inside the vehicle (trunk area) rather than an external ground which is more likely to corrode. And do this for both rear light assemblies at the same time.

Probably not a bad idea to clean the contacts once a year anyway, especially in wet, damp and salty environments where electrical contact corrosion is more likely.


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## SwissJetPilot (Apr 27, 2014)

Here's a few pictures of my completed earth (ground) retrofit project. Pretty straight forward really. Just get a nice piece of 2.5mm grounding wire, drill a hole next to the ground trace and insert a SST bolt so the head contacts the earth trace. Then attach your extra ground wire with a terminal ring connector and secure with a nylock nut as shown in the video.

I was not keen on using the exterior grounding points as they'll likely corrode over time. There are two perfectly good ground points (shown previously) conveniently located on the left and right sides of trunk and very close to both the rear light wire harnesses.

It takes a bit of work to get the extra wire through the wire rubber grommet, but the results are worth the effort. The pictures are shown just before I wrapped everything with a length of electrical tape just to ensure everything is weather-proof.


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