Alternator plug?

I have a alternator out of my 94 Galant LS (4G64 SOHC) that has 2 white wires that go to the battery (after fuse box) and a 2 wire plug with a red wire and a white wire.

I plan to use this alternator in a different car (95 Metro) as a second alternator to power the huge stereo. (~4000 watts)

All alternators I found for a 94 Galant say they have a internal voltage regulator, if that's true; what do these wires do? The Haynes manual says they go to the ECU but it doesn't explain what they do or why.

When the Galant was still running the alternator would regulate 14.4vdc with that plug connected, with it unplugged it would regulate 15.4vdc. So, I'm guessing its not really needed.

From what I have heard voltage regulators on an alternator determine when the battery has a full charge, afterwards "regulates" the charge being sent. If you don't plug that in the alternator may run at full power a all times, which with a big stereo it's good to keep the power flowing to the amps, but is not so good for the alternator. Alternator may heat up and give out right away, if not it will greatly reduce its life.

Thing is, the regulator is internal so it shouldn't have any wires outside the alternator. At least I wouldn't think there should be. If that plug is for the regulator, wouldn't the regulator be external?

Okay, I think I got it figured out now.

4awg wire to the battery (as always) then the plug, the thicker red wire should connect to the horn relay (to sense fuse block voltage) and the white wire connects to the dash's battery light.

Since I already have both those wires available on the opposite side of the block (on the stock alternator for the Metro) I'll just make a small harness that goes over the top of the valve cover and will tie into the factory harness. There is already a small harness that runs there for the oil pressure light and the temp gauge so I'll hide the wires with them.

That should work right?

Did you say one of the wires from the alternator plug goes through the horn relay? Just wondering because I was investigating AC compressor issues the other day and I switched the horn and compressor relays in the fuse box to see if that was the cause of my AC not working. Well, the horn blew with the relay that was previously in the AC spot so I just ruled it out, but now I'm having charging/starting issues.

I replaced the starter and the battery tests fine per autozone. I have to jump to get it started and after that the alt. charges well (around 14.6v), then drops slowly. I'm still letting it run and it's down to 13.9v after running for about 20 min. Anyway, now I'm wondering if swapping the AC and horn relays is causing my charging issue. Any thoughts?