Electrical Alternator?

[Dondre Richards]

I have a 2002 Base Mustang and the Alternator was giving me a bit of a problem. I took the new alternator out of a focus and put that one in the housing for the mustang. the Alternator works but only after i rev the engine up to 3000 rpm other than that the battery only gives me 11 voltage and slowly dies down but after revving the engine to goes up to 13v and works perfectly.