hi to all,

i have an 85 volvo 240 wagon, on the drivers side i have a seperate low beam and high beam.
when i turn on my low beams the drivers side works and on passenger side works, but when i turn on my high beams
both the low beam and high beam on the drivers side both go out, but both the low beam and high beam on the passenger side works
replace both bulbs and still no luck, if any one has any ideas i would appreciate it
thanks in advance
Jerad

 

Your headlight has a bad ground and is grounding through the other bulb. Now you would think it is on the side that is out but that is the one supplying the other headlight with a ground. Check your ground wires on both sides and I think you will find a bad one. Do you know how to do voltage drop testing? Negative side on battery - test the grounds with the positive red side with the headlights on. (It only works when there is current flowing) You should read very low voltage on the ground side (like 0.2v) If you see 3v or 4v you have found your bad ground.

 

By the way our beloved volvos are getting old and there are bound to be electrical problems. Most but not all mechanics are bad at diagnosing electrical problems (read expensive) I was at a total loss when it came to electrical problems when my father died (he was an electrical engineer and was kind enough to solve the problems for me) So I have been reading books on automobile electrical systems since and learned a little. Then I read Tracy Martins, "How to diagnose automobile electrical systems" Instead of giving you a desctiption of the system he gives you a nuts and bolts here is how you test it. This single book is worth its weight in gold bullion. I understand how this stuff works now and I never have before. It would have saved me so many times. If you want to learn about automoble electrical problems and how to solve them and you only want to read one book this is the one. Also the wiring diagrams offered by Volvo technical publications are worth it even though they are a little pricey. They even show where all the grounds and relays are.[:-]