Do a full field test, that will tell you if the alternator is capable of charging.
To do this:
Insert a small screwdriver or other pointed object in the D shaped hole in the rear of the alternator. This will ground the rearmost brush forcing the alternator to go into full field mode. This will bypass the regulator and the alternator will put out 100%. If it charges doing this your alternator is good. If not then look at the regulator or the wiring.
Don
