@curse, This is not as bad as it looks! It's stories.
I understand electrical schematics. After working on aircraft for years, it comes with the territory. And as far as I have looked at mine, a '74, it's part of the fuse block diagram either on the engine side or the cab side. On the schematic fuse block diagrams there are two sides, the engine bay side where all the wiring from the engine, lights, etc. go down to the fuse block that are all numbered, then the side that is on the other side of the firewall under the dash.
Unfortunately do not think these two are the photo opposite of each other because they are not in most cases! Where number 128, a size #20 wire (this wire is made up by me as an example) comes from the engine side of the fuse block goes through the firewall into the other side of the fuse block into the cab, comes out in the little square hole for 56, #18 size wire?? This should have been #128, #20 size wire that goes to whatever inside the cab. The only way to follow this wire coming from the engine side of the firewall is to unbolt the fuse block from the cab side of the firewall and pull it away to see where that wire ended up when they factory pushed it through, and what little square hole in the fuse block it went into, and then where it went inside the cab.
I found out after looking closely at my fuse block inside the cab that my cab side fuse block was UPSIDE DOWN!!! when the factory threaded the wires through! So where the field wire coming from the alternator comes into the cab into the fuse block was in the little square hole for the damn backup lights! That is if you were looking at the schematic and was assuming it was supposed to be in the correct little square hole in the fuse block that should have gone up to the little Red light that lights up on the dash the moment you start the engine, then turns off. That little light tells you your alternator is working right. But don't go and try to find where that wire is coming from the alternator into the cab, because you won't find it. Unless that is, you take the whole harness coming out of the fuse block, apart and dig around for it.
Of course you can use a power finder, or whatever it's called that has a wire with a clip on one end you hook to a good ground, and the other wire goes to a pointed screw driver looking tool with a light inside the handle. It lights up if you have power in a wire so you can test for good grounds? I can't remember what it's called, but that's my discription of it. Or a Amp/ohm meter tester you use for testing good circuits, shorts, power, ohms, whatever. We just call it an "ohm meter". You could do a continuity test on all the wires down in the fuse block but don't trust the numbers on the wires that the schematic shows it should be. If the wire shows dead it doesn't mean you're on the correct wire.
What I ended up doing was buying a spool of wire from a parts store and made up a set of clips I can put on wires, and clip onto the other end of the wire and it's like, 20 ft. long so I can test anywhere on the truck I need to test. Forget lights, testers, or meters. I just hook things up directly and if it works, it's good, if the light comes on it's good.
