Volvo 780 Headlight Issue

Hi all, hoping you can give me a sanity check to see if I'm on the right track in solving this issue. My 1991 780 has a strange electrical gremlin I'm trying to chase down, namely that the passenger side headlamp is very noticeably dimmer than the driver's side. In addition to this, the passenger side turn indicator bulb is continually blowing out no matter how often I replace it and clean the connector. To top it all off, when the headlight switch is in position three the windshield wipers turn on and cannot be turned off with the stalk. Pulling fuse #15 turns the wipers off.

I suspect this is due to a corroded ground on the inner fender behind the passenger side headlight, as after hours of perusing the wiring diagrams this is the only place where the headlight, turn indicator and wiper motor might cross. A dim headlight on one side only isolates the problem to that side of the car, and extra current is probably leaking across the ground into the wiper motor. Am I on the right track, or is there something else I'm overlooking?

If so, is there a special trick to getting to it? With the washer bottle and air box in the way, would it be easier to just remove the headlight to get to it, or is there an easier way?

Sounds like a ground problem, yes.

Disassemble as you find most convenient and clean/r&r as necessary. Pulling the air box and washer bottle is not really taxing, suggest this approach.

You are 100% on the right track, that is absolutely a grounding issue.

780 could be a little different but I wrecked my 760 turbo and that's the exact issue I had.

I would go over a bump at night and boom, windshield wipers.
I recall the ground block down there being accessible by hand. Just a quick jiggle would get me on the road again.

Thanks for the feedback everyone, I'll tackle the grounds this weekend and report back. Hopefully with photos.

Do a voltage drop test. Look it up. Or just dig in and clean and inspect grounds. Or run a tesr ground wire and see if it fixes it. I have done that for battery cables: installed a jumper cable in place of the ground wire for example and got a starter to go that wouldn't before.

There's a ground block on the inside fender just behind each headlamp. Remove them, clean them and reinstall. Yes, both sides.