Intermittant alt issue

[thealleyboy]

Hey Guys:

I'm putting a new one on the road, and the alternator guage is showing inconsistant readings...

The battery is known good, and the car hasn't failed to fire up yet. However (assuming that the guage is correct), the alternator is charging intermittantly; sometimes dead zero, and other times normal. Had Autozone test it, and they seem to think that the alternator is kicking out too much juice. Makes sense - except for the intermittant "normal" output.

Swapping a different alt is no biggie, but this is still bugging me. I suspect a bad diode - yet the intermittant behavior isn't making any sense to me.

Any theories??

thanks, John