neodenium

I have a stock 88 vert and a couple days ago my alternator died. I pulled the alternator, had it and my battery tested. The alternator failed and battery was good.

I replaced the alternator and for a second after starting the car, the internal voltmeter showed 14v, then all the warning lights flashed (overvolt warning?) and the voltmeter dropped to 12v. Pulled the new alt and battery again, had them tested and this time, the alt was fine but the battery was bad.

I replaced the battery, internal voltmeter showed 14v and I took it for a test drive. After about 3 miles, the internal lights flashed again and the internal voltmeter dropped to 12v. Pulled the alt and battery again, tested both, and this time, both tested good. Not knowing what else to do, I got a new alternator (diff brand) and put it in. Now with the new alternator, I'm showing 14v again, though I've only driven it for ~5 miles.

I'm hoping that I just got a bad alternator that for some reason was testing good at the parts store, but what are the other possibilities? There's continuity between the B-wire and the positive battery terminal and there doesn't seem to be a grounding short on the B-wire. Everything else seems to work fine, except for my cabin light, but that hasn't ever worked for me.