Well, on my 1984 Mustang GT-350 I originally started with a 1g alternator that wasn't charging. So I thought "well, it must be the external voltage regulator." So I swapped that out, and nothing. Just a 12v reading from my multi-meter.
So I thought, "damn, it may be the alternator!" So I took it to the shop to get tested, and ir read fine. I then decided I'd get cute and rewire a few things and set the car up for a 2g alternator, hoping that the internal regulator would solve my problem. But again, nothing. Same 12v reading.
It was then that I decided that I'd get really fancy and do the 3g swap. So I got a 3g alt and an old grinded down alternator bracket from my old 5.0 and did my little rewiring. Again, nothing. Just the 12v battery charge reading.
So I did a little more research on them internets and read about a certain 500ohm resistor that the green wire from the alternator is supposed to connect to in order to tell the alternator to start charging. I followed the green wire and then foiund that it wasn't attached to anything behind the dash. Not knowing exactly where the resistor is supposed to be behind the cluster I had to wire my own solution.
So this is what I did. I wired a 12v key-on power source to the green alternator wire with a 500-ish ohm resistor in between them. When I started the car and took the reading from the alt it showed 14.7v. Problem solved. Oh, and ignore the twist connectors, I'll be wiring it all up better/permanant this weekend.
I would however like some advice on a few things, like where the resistor is 'supposed' to be. For the life of me I couldn't find that stupid thing. On 87-93 foxes i think they're wired near the battery light on the cluster, but my 84 doesn't really have one of those. Any ideas where it is?