[RETed]

1) The 12VDC reference wire (which you call a "pin") needs to be connected to +12VDC constant, direct to the battery.
This is applicable to the FD and Kouki FC alternator circuits; prior to that, the Zenki FC alternators were only wired to switched +12VDC.
This tells the alternator what the status of your battery is.
Try not to connect it to the +12V post off the alternator, cause it'll be higher than the battery + post, and there's chance that you get back EMI from the alternator operation - this is why you don't see the OEM's wire it to there, even though it's a short shot.

2) The other pin is for the idiot light.
Like others who have already said, it's not necessary to connect this to anything.
This just completes a circuit (to ground?) so your idiots lights light up when the alternator fails.

As for your problem...
I had the old silverrotor FD alternator, and it always had a major drain with the engine off.
I bandaided the situation by resetting my circuit breaker anytime I left the car off overnight.
I traced the problem to the alternator sense field not dropping even after turning the ignition key off; for some reason when I dropped the +12V reference, this would drop the field and killed the excess current draw immediately.
I just chalked it up to a crap rebuild (these things were rebuilt by silverrotor by some shop).

Once I replaced with another unit, I NEVER had that problem anymore.

So it's quite possible you're in a similar situation.

It could be possible that you have a shorted diode in the rectifier, which would cause the alternator to keep draining voltage with the engine off too.
I've fought this problem with my MX83 alternator, because I think the 15VDC+ levels my battery charger was giving it when I had to jump it.
In this situation, every time you reconnected the alternator, the current draw would always be too high.

It's very easy to troubleshoot these things, as you need someone to measure current - most DMM's do this.


-Ted