Any ideas on this odd electrical issue?
 

Hello

I changed my day running light bulb the other day on my Volvo 740 (1989 B200E) after months of it being out of action. When I turned the car back on, the day running lights didn’t work nor did the dashboard lights.

Since then it hasn’t changed. When I turn on the lights the rear windscreen wiper goes on and the dashboard lights up. All fine if it’s raining otherwise my wiper will be worn out! When I turn the car off, the radio doesn’t turn off unless I switch it off manually (it’s an after market one which turned off automatically once the ignition was off). In addition the seatbelt warning light doesn’t turn off unless I turn the radio off. When I indicate left it also sets off the rear windscreen wiper for one wipe.

I have checked the wiring by the replaced light (by the air filter box) and looked for bare wires but can’t see any. I can’t see how changing one light can cause so many problems! Does anyone have any ideas?

Thanks in advance.

Is it a facelift or pre-facelift car? Only makes a difference to the bulb needed for the DRL/sidelight bulb but everything else you're describing is pointing to a bad earth somewhere and/or a short on the +12V side and/or missing/blown fuses.

Check all your fuses for condition and security, likewise with the relays behind them in the fusebox. If there is any doubt over a fuse, even if it looks good - renew it. Seriously, i've come across so many faults caused by fuses that look ok but in fact aren't i could probably write a book!

I need to go out now but will look later to see if there is anything that might be common to the problems you've mentioned - out of curiosity, if you unplug the stereo, do the faults disappear?

Thanks. It is pre facelift. I tried the fuse out for the radio and still set the rear windscreen wiper off. Could it be the earths then by the air intake? I must have knocked something when I changed the bulb.

I’m no mechanical engineer or electrician but can do common sense stuff so helpful for any ideas. Thank you again.

When i said unplug the radio, i did in fact mean unplug it - it's possible there's something in it linking something together when it shouldn't.

You should have the twin filament bulb if it's pre-facelift in your DRL/sidelight, are you sure you fitted it the right way round? The pins are at different heights for this reason and if it was a struggle to get it into the bulb holder, it might be in the wrong way round.
However, it won't necessarily cause the problems you've got.

Check that earth point as you suggest for any loose, disconnected or dirty connections. Also check ALL the fuses, even seemingly unrelated fuses. There is a backfeed somewhere, why/how remains to be seen.

Well- that was definitely a weird one. I unplugged fuses and eventually managed to trace it to the left hand side main bulb - when the fuses were in,it would set off the wipers and other stuff.


I unplugged the main bulb and checked the bulb was in correctly- it was. Made sure it worked by popping it onto the right hand side- it did. I put it back in to the left hand side and put everything back in - popped the fuses back in and it all works fine.

Thanks for your help. It seems to be cured. Maybe it just wanted a bit of tic?!

On experience, i would say it was a poor earth connection on the bulb causing a backfeed as i suggested earlier - well done on finding it! :thumbs_up: