My alt light stays on, but quite dimmly. It does get brighter at times, but nothing I can pin down to match load/rpms. Back when external reg alts were common, I used to know what caused this, but have forgotten. Is it the diode trio failing ?? or the brushes worn down to the springs and the charge being limited by the spring ?? The light is off when the key is off. The battery has stayed charged thru all this and always cranks the engine over very well. I have started it 2 dozen times and driven it about 200 miles so it is charging.
Thanks for any insight........:thumbsup:

Could be bearings, a diode or bushes
Time for a rebuild

Yes a diode trio failure can cause it. There are three phases in the alternator. If the diodes for one of the phases shorts or opens for example, the alternator can still charge, though not as well.

Yes a diode trio failure can cause it. There are three phases in the alternator. If the diodes for one of the phases shorts or opens for example, the alternator can still charge, though not as well.

Thanks, that was my foggy recollection too, that a dim light was caused by the diodes. I did find replacements for them online, so I will probably pull it apart and rebuild it. I'm sure it isn't the original, but the date code is about 9 months after the build date, so it could be a warranty replacement.