I dunno? It blazed up the rubber insulator on the charge terminal, which comes off the regulator - through the aluminum case of the alternator. The glass-fiber insulator that the cable bolts down to on the post melted, the charge wire was glowing red-hot and visiby doing so in broad daylight.

I suspected I was missing a ground somewhere, but they were all in place. The battery I was using sat on a concrete floor for a year (dead), and I slow-12v charged it for an hour and a half before re-installing it... it tested good.

Since both of those were the only parts re-used on my car (and the alternator had already been rebuilt twice within 3000 miles), I just went ahead and replaced them. No problems since. I don't get it. It was the kind of fire that I smelled, popped the hood, went "WFFFFF!" and blew it out. I'm getting a fire extinguisher today. I've been stupid for not having one already.

The car runs great, though... before and after. I just have some pretty big boost leaks to sort out. Something in the idle control system and emissions system quacks when I hit 10 PSI.