I have a S5 alternator (nice 80 amp) on my car to go with my S5 engine swap. Part of the deal with swaping alternators is changing to the new style plug introduced on the S5.

First, the batery warning light does not come on when I try to start the car. Keeping mind I no longer have the stock ECU, so I dont know if the light is independent of the 85 ECU or not.

Second, the Voltmeter in the dash shows 12volts untill i rev the engine to around 2500rpm, and then it jumps to 14 volt. BUT when I turn the car to acc so the volt meter stays on, it still reads 14 volts with the engine off. If I turn off the ignition switch, and then put it back on acc it goes back down to 12 volts.

I have driven the car for a while, so I know the thing is working, but it really worries me. I dont know if the thing is charging under 2500 RPM or not. ALSO I forgot to mention that I have a racingbeat underdrive main pulley. I know this slows down the alternator, but I'm wondering if it might be causing my 2500RPM start charging condition.

 

bump

 

I had a stock one on an 83 that was acting the same way. Would not start charging until you reved high one time. I bet it is a product of the underdrive pullies. Alt could be going bad also.

 

Yeah the alternator is used.... Did your 83 have a underdrive pulley?

 

no. It was just going bad. I changed it when I changed the engine and did have any problems after that. Try taking off the pully and see if that corrects it.

 

haha easier said than done. I have the racing beat main underdrive pulley. That thing replaces the main pulley hub. I'd have to put on the origional hub, AND get new belts....

But it looks like a new alternator will be on my list of things to do.

 

Could you put the alt on a friends car? Would be a good way to check it.