Okay so 94 powerstroke, alternator tests good on the bench test, put it on the truck and i am only getting intermittent charging. Batteries both test good, just changed out the plug on top the alternator...

While changing the plug I thought I would test the wires, full voltage on the yellow, and on the green/red tracer nothing, and then 12+volts. When that wire gets the 12 volts the alternator starts working and charges fine.

So I am assuming that is like an exciter wire for the alternator but where does it come from and why would it only be getting power sometimes?

Please help...

 

GRN/RED goes up through the Alt light in the dash then to the ignition switch. Here is a diagram that might help ...



A - terminal YEL/Wht should be 12 volts (battery).
S - terminals (jumper) WHT/BLK should be about 1/2 battery voltage.
I - terminal GRN/RED should go to 12 volts, otherwise the alt light in the dash would be on, is it?

Sounds like a bad connection or regulator.

 

light flickers and is on solid sometimes... Had the Alt tested, it tested fine but we replaced the regulator with 2 other new ones and it produces the same results.

there is no voltage coming through that wire at times... then other times I could get 12 volts on it... bad connection somewhere?