dim alternator light below 3k

[treed2 at wsu.edu (T. Reed)]

Hi all,

I'm guessing that this has been covered before, but I did a search and 
couldn't find anything, so here goes..

I came home late from work a couple nights ago and it was dark enough 
outside that I noticed the alternator warning light was dimly lit. It's 
not bright enough to be visible in the daytime, but at night it glows very 
softly until the engine is revved above 3000 rpm where it abruptly turns 
off. From 2000 to 3000 rpm it starts to dim.

Everything appears to be in order with the alternator mechanically.. and I 
have beefy ground wires run all over the place, including directly from 
the battery to the alternator casing. Is there a standard culprit for this 
problem?

Thanks

-Toby