So I accidentally hooked a battery up backwards (yeah, I know, I'm a dumbass) and now when I'm at high rpms my volt gauge goes up to 15-16V...

I assume I've fried the voltage regulator in the alternator? are these replaceable? or do I need to just get a new alternator...

 

I believe FC/FD voltage regulators are replaceable. These guys had all of the rebuild parts for the FC/FD alternators, last time I checked Arlington Armature - Since 1947. I was inclined to do a full rebuild, but a remanufactured one from Ray Crowe was cheaper.

 

Sounds like the voltage regulator crapped out. I would stop driving the car asap before something else fries. I offer a rebuild of the alternator and an upgrade from the stock 90 amps to 140 amps. Pricing is $215. Let me know if you would like one.