Working on a 1989 Ford F700, witha 429 gas motor. Got it from a previous owner and wiring is all messed up. Took wiring harness that feeds alternator, oil sending unit, coil and completely went through it. Alternator will show charge for a short time then will quit. There is a white wire coming from the alternator that leads to a plug that leads to another plug and what I can figure out it is not hooked up to anything. Wondering if this is the field wire that should be reading voltage of the battery.?? Also fuel gauge does not work. Any wiring diagrams or knowledge would be helpful.. Thanks