Hi all I bought my truck with a few issues namely the wiring. It never charged despite the seller putting in a new alternator. I got rid of all the extra crap the previous guys had spliced and cut and found a few completely burned wires in the main harness inside the cab. I threw out the universal turn signal and its wires and installed a reproduction assembly, replaced the printed circuitboard and voltage regulator for gauges and upgraded to a 3G Motorcraft alternator. Everything's been going well except I can't find a wiring diagram for a 1973 (this site has 1974+) so there are some differences.
- I connected the 3G alt. to the light green with red wire. This has no voltage so my alternator doesn't kick in. I jumped it and was able to get a charge so I know this wire is cut somewhere.
- Inside the cab the factory splices the green/red wire with a red/yellow stripe wire. This goes to the ammeter but I don't know if there is a "return". So not sure how my ammeter is working but that green/red stripe wire is just dead.
- There was a blue wire, maybe with a white stripe from the engine bay into the main harness that was completely melted so that's also a mystery.

Main question is, how do I properly trace that wire? I removed the harness completely and the green/red wire goes into a factory splice (looks like a rubber cylinder) where different color wires come out (red with yellow stripe)
Can I wire this green/red stripe wire inside the engine bay and just bypass the cab? I know that according to 3G upgrade instructions it should go to the "Run" ignition switch but it definitely does not go to the ignition switch it doesn't make it that far into the main harness before that splice. Or did it? My truck has an aftermarket replacement ignition switch pigtail so all the cables coming out of it are black, and hooked up at least to the 1974 diagram instructions. Is there supposed to be a green/red wire there? If anyone has a diagram specifically to a 1973 F250 I'd appreciate it. I have all 5 volumes of the Ford service manuals for this year but they don't have diagrams. Not even the Electrical & Chasis volume.

 

I have a Haynes manual and I think it has 73 wiring diagrams. If I make it to the shop today I'll snap some pictures of the diagrams and either post or I can email them to you whichever you prefer

 

 

Where did you connect the wire from the small plug on the alternator? I think it's called the trigger wire, but I'm not remembering off of the top of my head where it should go.

If it starts charging when you increase the engine RPMs, then it could be working properly. You could always throw a smaller pulley on the alternator, to make it spin faster and charge at a lower engine RPM.

 

I'm hooked up exactly like the diagram below. I can trigger the alternator by putting voltage to the light green with red stripe wire just fine, so its not the alternator or anything other than me having a dead green/red wire. I have an ammeter in my truck so no dummy light. I don't have a resistor hooked up, but then again that wire doesn't lead to my ignition switch anyway it goes in to a factory rubber cylinder splice and comes out a different color. Red with yellow stripe that goes to the gauges. Thats why I don't know what to do, because my ammeter works.

 

That splice in the rubber block sounds like where one of the ammeter wires connects. Do you have continuity through that splice you found? You said that splice is in the cab?
On my truck, I found a splice like that near the starter solenoid, and it had a wire broken off flush with the rubber. When I reconnected it, my ammeter started working.

You ammeter circuit is basically a bridge or shortcut, (shunt) along the charge wire. You can disconnect the ammeter wires, and it will still charge. But if you cut the main wire which is being bridged by the ammeter circuit, then all of the charging current will pass through the ammeter for a few seconds, until the ammeter melts down.

I think the principle is that the one ammeter wire goes to near the battery where it samples battery voltage, and the other ammeter wire goes to near the alternator, where it samples charging voltage. If one side is higher, then it will move the gauge needle.

My working ammeter is the one thing keeping me from throwing a 3G into my rig, but the 1G setup works fine and I don't have any power-hungry accessories, so I'm not worried. OEM Ford ammeters and 3G alternators are said to be incompatible, but I suspect that there is a safe way to have both - I just wouldn't know how to begin to wire it up.

But I think you're safe to just run your own wire to an ignition-On circuit of your choice. I did the swap on my Stang, although it had a 2G internally regulated alt, and I guess I must've been able to use the car's existing green wire - I can't remember. I guess I could go out there and look...