On parts monkeys and alternator and battery testing. I bought an alternator, installed it, was horrible. Took it back, they bench ran it, declared it good and me an idiot. Whatever, exchange this one. Put it in, they check my car and told me the battery was bad. But, no more charging system faults and that battery and alternator took the car to the end of its life. I have also started running a second ground from the alternator body to the negative terminal, just as insurance.