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Strange Brake Light Problem?

483 Views 5 Replies 3 Participants Last post by  ChriberV8
Hello! New to the forum, and new Touareg owner. (2003 V8).

I have encountered a very strange brake light problem.
My right rear brake light stopped working (legislation station pointed this out + got 6 weeks to fix before not allowed to drive).

So, I bought new bulbs.
None worked. (still normal back light and indicator worked. Also brake light right rear and 3rd brake light worked fine).

I got the multimeter:
Measured connector, then the backplate connected to the connector (where bulbs are mounted). Power on normal rear back light lead.
And when braking power on the break light lead (!?).

I switched to a spare bulb backplate.
Same result (!).

And for Both backplates, as soon as I put the bulb in the backplate, the rear back light is litten, But, the brake light does Not work when braking!
I tried to get the backplate leads push up much more forcible to the bulb leads, but no difference.

When I measure the brake light lead, without braking, I get a strange result. 4-5V on the Multimeter.
Now, it would be possible to have a diagnos bulb test this way, but is this not a bit far fetched?
It would be as easy to make the diagnose run when brake pedal is depressed, and when 12V is applied to the bulb?

Another thing is that, the indicator chime/tick has disappeared, and at the same time I get no more warnings in display for broken bulbs.

Anyone having any idea of what this could be?

  • ECU locked up? (does any ECU run the rear brake lights?)
  • Diagnose ECU not working that interferes with the function?
  • The 4-5V shall not be on the lead for the brake light when no brake is depressed, indicating short circuit on the wire harness?

I would be very happy if anyone has any similar experience, and clues to what could be wrong!

What a community! Impressive! :)(y)

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What bulbs did you get and use? Only the P21 4W ones will work.
If you have correct ones, then check the where the plastic w/metal leads mount to the light assymbly as I believe there are some small screws or connections that hold this together that may have come loose or broke and need some attention. I had to run a screw in mine to hold the plate in place for good contact as I had tried to replace the bulb multiple times to find out it was the connection.
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