A4 rear lights don't work when main beam is on. HELP!

[AnniinaW]

Hi guys,

I’d really appreciate some help with my Audi A4 B5 from ‘98. I have a problem with my rear lights. I took the car for an MOT and it failed because the rear lights go out whenever the headlights are switched to main beam. I hadn't noticed this during the summer because I never used main beam!

The rear lights work just fine on sidelights or normal headlights, the problem only occurs when main beam is activated.

I should mention that I have aftermarket headlights on the car (Devil Eyes by Dayline) and that on the left side the LED strip stopped working during the summer (not sure if that is related or not). I replaced the headlights because I needed to change to LHD pattern ones having moved to Finland. I did try to get standard headlights twice but both places delivered the wrong headlights so I kind of ended up with the Devil Eyes because they were available (getting parts here can be difficult). I no longer have the old headlights or I would be able to swap back to them as a test.

Could the headlights be causing this problem with the back lights? Has anyone experienced a similar problem before?

Any help would be appreciated, I need to retest the car in a couple of weeks and nobody locally seems to be able to help me.

Thanks,

 

[AnniinaW]

Well, I guess it was a long shot. The MOT ran out and so the car is pretty useless to me now. I took it to Audi and they told me the wiring was fine. They kept the car for nearly 7 hours and couldn't find out what was causing the problem. I have no idea how to fix this now though. No auto electrician will touch it, one guy even told me not to bring the car to him. The car is mechanically sound and according to Audi the wiring is just fine so I feel at a loss to fix this. I can't even sell it without the MOT. I really like this car though, and I just remembered how much I hate the bus! Is there really nothing I can do?

 

[aragorn]

unplug the headlamps from the wiring harness, and then see if the problem continues!

Do the front sidelights also go out? Obviously these will be harder to see, but if so it infact means ALL the sidelights are going out when the fault occurs, rahter than just the rears, which makes a bit more sense and likely points at a faulty stalk.

 

[AnniinaW]

Hi,

Thanks for the reply. I tried to test the lights by unpluging the headlamps as you suggested but I couldn't get the left side undone. I removed the wire clip that holds the plug closed but it was stuck I think. Maybe it was frozen, but I will try again when the weather gets a bit warmer or I can park the car inside (not much fun doing this in -20C!). If the side lights do go out as you said then I think that I will just replace the stalks. I did wonder about the stalk myself though, so I am wondering if it is worth the risk and just replacing it anyway. If that doesn't fix the problem then I guess I need to replace the head lights too... Thanks for the advice, I think that it will help me diagnose the problem.

 

[AnniinaW]

unplug the headlamps from the wiring harness, and then see if the problem continues!

Do the front sidelights also go out? Obviously these will be harder to see, but if so it infact means ALL the sidelights are going out when the fault occurs, rahter than just the rears, which makes a bit more sense and likely points at a faulty stalk.

Hi,

I checked last night and the front side lights do go out when I put main beam on as well as the rear lights. I have ordered a new stalk from Audi and I will fit it tomorrow or Thursday and let you know if that fixes everything. Thank you very much for your help!