[bourbon]

dont know anything about the alternator you have. have you hooked up a voltmeter to the car so you can see where its at while running (charging)? you should be up in the 14 volt range.

when you say battery light comes on do you mean the ALT light? sorry but i dont drive my mustang much anymore so if there is a battery light you will have to forgive me. if the ALT light comes on it means your not charging the battery and your alt. is to blame. did you ever think that maybe your old battery may have been bad due to a bad alternator? is your belt slipping around the alt.?

also, dont be connecting or disconnecting the alternator wires while the car is running it could affect the computer or other circuits. EFI cars are sensitive thats why i have a love hate relationship with mine.

oh and if your car has a factory voltmeter dont look at it cause im sure its wrong. use a digital voltmeter.