As for the wiring, makes sure the alternator is properly grounded to the block. Run an extra ground wire from a bolt to the block with a good clean connection and see if it helps. I had it happen once on my car, and even though everything looked good, an oily/paint surface in between the mounting ears of the alt and the motor/mounting made the regulator freak...
if not, don't give up, electrical problems can sometimes turn up to have the weirdest sources...