You can check the alternator voltage output with the ohms meter while the car is running.Ground the black lead to the alt housing, the red to the large post on the back of the ALT.With the ohms meter turned to the proper setting.This will tell you the voltage the alt is putting out. 14.2-14.8 volts is ideal. It really needs to be load tested though, AUTO ZONE [X(]Oh yeah, the alternators I build will idle at 100+ amps.