that connects to small stud with 8mm hex nut on alternator. Alternator won't charge unless this wire is connected. When alternator rpms exceed idle and the alternator is charging, the current flowing through this wire stops and battery warning light on instrument cluster turns off.
Ok, that makes sense but confuses me. There is another wire that terminates in an eyelet that I thought was this wire. Now I gotta figure out what that wire is.
There are three back there - yellow, green/grey(black?), and one other. I can only identify two studs... the solenoid and the alt energize. Any guess on what the third position is that I've overlooked?
as you've figured out. Black (blue?) wire may attach to the oil pressure switch located behind starter. This can be confirmed by grounding it and seeing if the instrument cluster oil warning light illuminates. Light should go out when wire is removed from ground.
The oil pressure switch has an actual connector on it, so that's not it.
I pulled it out into daylight today and I'm pretty darned sure it's not factory... the terminal at the end is suspect... and there is no obvious purpose for it. Guess I gotta go dig through the car....
Answer is that the black wire terminates at a momentary switch under the ACC. The other leg of the switch runs to the positive distribution block. My guess is the button was intended to operate the starter... maybe to bypass the ignition switch, starter relay, or range sensor. Now I gotta figure out which.