I have a 86 4Runner, and have been having a strange electrical problem. While driving or idling at night the headlights and dash lights will dim for a second or two and then go back to normal. It seems that there is some sort of pull on the motor because I can also hear the motor idle down when this happens. If I leave the battery hooked up over-night it will be dead or almost dead by morning. Also my rear window will not work since this problem started and to add to the mystery, when the battery is really low a strange buzzing noise occurs and is coming from inside the body just behind the driver's side seat. I had both the battery and alternator checked tonight and they both are good. Can you help?

 

Have you checked ALL ground wires for corrosion, exposed, frayed or loose?

 

I don't know much, so don't expect much from me, but I think you kinda narrowed down a problem here....that the window won't work and the buzzing and the drain.

the relay box (not sure if that's what it's called), but the box for the rear window sits on the driver's side just rear of the B-post at about the level of the passenger in the rear. you would have to do some searching to see exactly what goes where inside of that, as I do know that there is a culprit relay in there.

also, that rear window itself is a nice place for moisture to accumulate and perhaps you need to examine the condition of the wiring in there.

 

Thanks guys, I'll check into those things.