You are correct in assuming that wire from I terminal comes from the ignition switch, then thru indicater light then to regulator. It would appear that the ignition switch, or the wire is at fault. See diagram below.
I dont think you will have to go that far. If there isnt any power coming from the switch to that wire, when in the run position, its the switch.
Best of luck my friend!
Do you have any further questions?
Man i got dizzy reading your last post above :-)
The oil pressure doesn't make any sense to me,,,NEVER heard of such a thing with the charging system.....
If you jumper power to the " I " terminal when running does it charge?
You assumed correct. If the alt doesn't charge when you full field it, it will need replaced. Do that first, then check it and let me know. The current works weird if something in the alt is shorted and may be preventing current to that terminal,,,not sure as of now....
Depending on the color of the "motorcraft" trademark on the alt will determine amp output. See choices below. I would think a 70 or 100 amp is what it came with. Probably the 100
The main thing is that it's charging ok if it's between 14-15 volts. To be honest with ya, i would really have to be there to look it over to get a better grip on this. Kinda hard to wrap my noodle around it from here :-)
Best to ya my friend!
Sounds like you are really having fun now.....i'm out of ideas, but i will ask some of the other experts if they might know.