Hello folks,

I am seeing some mysterious behavior when I brake with "headlights on" on my 1991 740 SW.

With lights off, when I brake all rear brake lights work (rear driver side, central, rear passsenger side).

However when brake with "headlights lights on", on the dashboard I see an icon citing some lighting issues.
On the rear, I see that only the central and rear passenger side light go . The rear driver side does not.

Some extra and possibly redundant information. When I switch on headlights, the driver side light becomes on but when I brake only then it goes off. The rear passenger light becomes bolder when I brake. The left side switches off completely.


Any ideas/hints on how I troubleshoot this problem.

 

look at the bulbs, some have 2 filaments and wierd sttuff can happen if one lays on the other.

 

Thanks Bigdaddy!

I looked at the bulbs and replaced it just to be safe and it still had issues. Any additional things I should look at?

 

Look at the rest of them, they can throw some off. There is a relay in the system it could be bad.

 

I had a weird lighting issue awhile back; the engine would die if I switched on the headlights, sometimes only if the high beams were on. It got to where the only way I could drive the car at night was if I unplugged the driver side headlight. I would probably still be searching for the solution, or, more likely, would have paid some master Volvo electrician for a cure if I had not stumbled across a thread - I think it was on Brickboard - that lead me to a ground strip on the inside fender well near the headlight. Tightened/cleaned a few connections and everything was good again. I have since learned that a whole bunch of electrical problems are related to grounding points that are hidden all over the car (some are very well hidden). Unfortunately, I am a long way from locating most of them..

 

That sounds like it could be the issue said by Joseph for you Vipul