ProZ and I were typing at the same time.... Hard to tell without a schematic, but my first thought is you blew a fusible link by shorting the alternator to ground, or perhaps the internal regulator on the alternator. The alternator obviously works as you're seeing 13.4 volts at the battery. I would probably take the alternator to a good parts store and have it checked if it were mine, then start looking for a wiring diagram to see what components you're dealing with...