alternator not charging the battery

Check for power at the main terminal of the alternator with the key OFF. If you have no power there, check the fusible links at the starter.

One of the wires on the switch plugging into the external voltage regulator shows a light when I test the wire, and only one works when the same wire is coupled with another via the fusable link. Is that normal? Does that mean the fusable link is bad or the wire itself?

External regulator? That shouldn't have an external regulator and I'm asking about the power output terminal at the alternator.

Sorry, your right. It is actually the internal voltage regulator. The power output terminal is still hot. I tested that wire with the light test, and not to mention I touched a metal flat head screw driver to the output and it sparked tremendously. I am guessing that means it works although I have not yet checked the fusable link attached.

I hope you tested that with the engine and key OFF.

You should have power at both red wires with the key off and the brown wire with the key on. If the brown wire is dead, check the "gages" fuse (10amp).

I did test it with the key off. The small brown wire does work with the key on, but the thicker red wire never shows a light with the key on or off. There are a couple of fuses completely out and one where only 1 side works. When I put a new fuse in, the new one doesn't work either. I followed the thick red wire and it gets coupled with another wire via a fusable link; on the other side of the link, the wire puts off a light when doing the light test.

That sounds like the link is burnt out if there's only power on one side of it

Thanks so much. I went to a local salvage yard, and for $8 I purchased a fusable link and the alternator now charges the battery. I also want to mention that the heat/air/defrost system also stopped working and those too are running normal now. Thanks for the advice.

You're very welcome