I have a 91 Z with a v-belt system running only the water pump and Altenator. The altenator is a one-wire set-up. I've had the car running for about 1 month now and I'm on my 4th altenator. When everthing is good I'll have 14 volts at cruise and about 12-12.5 at idle, which is normal, but when they go out, it seems I'm running on battery voltage no matter what RPM I'm at. The wierd thing is that when I disconnect the battery, the guage will shoot to 14 Volts (while the vehicle is running) and I know there's amps cause my fuel pump and electric fans are on. I have the altenator wire running to the starter along with the battery terminal. I am a little suspicious of the battery cables, but my question is, have any of you ever heard of this or have the slightest clue as to what could be going wrong? I load tested the battery and it was good, plus I have no problems starting the thing. Bad wires? Short to ground? Coincedental bad altenators? Any help would be greatly appreciated. Thanks.

 

Very weird!
The only thing I can say is: Don't trust the dash voltage gauge, they lie.
Use a Digital Volt Meter(DVM) to measure the voltage at the battery. I also like to measure at the cigarette lighter to read the true voltage when driving.

 

Also make sure the connections are clean and tight at the starter.

 

Im having the same problem but im using a OEM 91' alternator. Heres my post

My Charging Problem