M998 Voltage Anomaly

[Jon0249]

1990 M998 A0, 6.5, 60a Alt

Drove to the farm, nothing unusual, all gauges dialed in as they should. On the way back, the volt meter, which is always in the green zone, dropped down about 1/4 of the way into the yellow zone once up to op temp. Got home, cooled down for 15 min, restarted and back to normal (in the green). Voltage at alternator with engine running = 28v. Voltage at jump start terminal, engine not running - 25.2v.

Any ideas why I might have been in the yellow, now back to green? Would temperature affect this? All terminals tight, no corrosion, no added drains on the system.

Thanks in advance.

Jon

 

[NDT]

Possible intermittent connection to the alternator excite wire, but most likely the alternator is on it's last legs.

 

[Jon0249]

Ugh. That was my worst fear, but not really that surprised.

Are these alternators rebuildable? Brushes, bushings, regulator?

 

[NovacaineFix]

could be a bad ground as well, but the alternator would be a good guess like NDT suggested.