Hello gentlemen. I have a new addition, a 95 F-250 SC 4x4. 4" skyjacker, 5.8, headers/ custom exhaust, edelbrock intake, bbk throttle body..... just bought truck. Alternator wasn't charging. Replaced with a new, not rebuilt one. (95amp) At startup, seems fine, 13.8v idle, 14.5 3/4 throttle. After a few minutes, output gets worse. Turn on lights, radio, ac, down to 11.6, 12.2 at 3/4 throttle. truck starts fine, runs well, battery load checks ok. Looked through some old posts for help and yes, green wire has batt voltage, good continuity through jumper. Alternator gets very hot as well. I ran a couple separate ground wires, batt to alt case, body, frame, block, etc. No change. Cant seem to figure why alt is working so hard. Even talked parts house into swapping out alt for another to double check. I need to lean on y'all for some guidance.

 

Is it an original style alternator with an internal regulator? Or did someone swap an external regulator style setup onto it?

 

If you have a good ground and power on the green/red exciter wire then you most likely have a bad alternator. Just because it is new does not mean it is a good one.

 

Sorry guys, busy day. To answer a couple questions, it is an original 3G style alternator. I did go back to parts house and change it out for another. No change. Still charges initially at startup, but gets super hot fast and with increased load, output goes way down. Red/ green wire has a good 12 volts. No evidence of a short anywhere. I do have a twin electric fan setup, but that should not affect system much.

 

If you have exciter power then the alternator is sending out as much power as it can. You have a serious current draw somewhere. Never under estimate how much power those twin fans can pull. They may not be the root cause, but I suggest you start pulling fuses until the output jumps up.