I promised someone (don't remember now who it was) that I would check the
markings on my Geo alternator and let them know the wiring of the pins.  This
is based on how the auto-electric shop labeled my alternator.  If anyone
should know, they should.  Rebuilding alternators and starters is the lion's
share of their business.  

Looking at the rear of the alternator, the pins look like this... |_|

The left vertical pin is marked "L", which is for the idiot light, I'm not
sure if it would go throuh the light to +12v, or to ground.  You would have to
check on that.

The bottom one has a zero with a diagonal line through it, which I take to
mean that it isn't used,

The right vertical pin is marked "Ign".  I believe this is to be a switched
12v (I didn't tell him it was for an a/c).

There is a large stud that goes to the battery.

Hope this helps.
Mark S.