I've been trying to get the Mustang ready for the dyno, and I've been having persistent alternator / charging system problems. I've gone through three alternators now, and they all had the same problem: they don't seem to be charging the battery even though the idiot light seems to be working properly (key off indicator off, key on indicator on, engine on indicator off). Key off battery voltage is 12.6, but it drops to 12.2 when the engine is turned on, and revving the engine up to 2000 rpm doesn't change the battery voltage at all.
I've verified that the black and orange positive wire has continuity with the B+ terminal, and the alternator case has continuity with the B- terminal. I've checked the fuse in the junction box and the fusible links (both visually and with a multimeter) and they all seem fine. I've also checked the yellow and green wires going into the alternator by back-probing the connector. They read as follows:
Key off:
Yellow/white: 12.6v
Green/red: 0v
Key on:
Yellow/white: 12.2v
Green/red: 1.6v
Engine on:
Yellow/white: 12.2v
Green/red: 11.2v
Needless to say, I'm stumped. The only thing that looks sketchy is the engine on green/red measurement, but I'm not sure what to make of it. Any ideas?
I've verified that the black and orange positive wire has continuity with the B+ terminal, and the alternator case has continuity with the B- terminal. I've checked the fuse in the junction box and the fusible links (both visually and with a multimeter) and they all seem fine. I've also checked the yellow and green wires going into the alternator by back-probing the connector. They read as follows:
Key off:
Yellow/white: 12.6v
Green/red: 0v
Key on:
Yellow/white: 12.2v
Green/red: 1.6v
Engine on:
Yellow/white: 12.2v
Green/red: 11.2v
Needless to say, I'm stumped. The only thing that looks sketchy is the engine on green/red measurement, but I'm not sure what to make of it. Any ideas?