Pull the alternator, have it bench tested. If it's the regulator, that can be replaced by you for about $15. If not...there are alot of places that can rebuild it for about 50 to 60$$. If you want a new one, make sure you get an exact match. Make sure before you get it home it has the correct pulley setup as your original. If the test killed the engine completely, it is running strictly off the battery.