i installed a gm alternator in my 79 and everything worked fine. i swapped it into my 75 wired the same way and it wouldnt shut off. even with both battery cables removed and the key shut off and removed from the ignition, the truck was still running, until i unplugged the alternator. it only has the charge wire from the alternator to the starter relay (battery positive) and the exciter wire going into the cab. Had to unplug the exciter to get it to die. It does not need that wire to charge above idle. but it worked fine in my 79. was the 79 factory ford wiring different that the 75 somehow? Sorry this might be kind of hard to follow.
First of all what are you thinking putting a government motors anything in a ford no wonder it doesn't wanna work LOL go to your local automotive electrical shop they should have a direct plug in diode that goes in line with the gm plug .plug it in and presto it'll shut off!!! they some time's feed power back through and allow the ignition to stay powered up
i used it because they seem to last longer in the mud and i got rid of about 20 ft or so of wiring to clean up the engine bay. That seems to be what it is doing, but why would it do it in the 75 and not the 79?
Thanks guys! I will have to do some more checking with the voltmeter this weekend when i get back to the truck. Tracing wires is simple now. I have removed everything i didnt want or need and have the harness unwrapped at the moment. Didnt get around to taping it back up last weekend.