How to test 1984 MerCruiser altenator has a red and purple wires coming out? I had the alternator rebuild in March 2012 only had it out about 6 times since repaired and was charging first time or two out. Took it back to shop today and they said it was working. I have over 12v on red wire going into alterantor but nothing coming out. My battery runs down when engine is running. Engine will die when remove + plus cable from battery. I'm at loss as what is causing my problem. Thanks for your help.!!