Hello all...
The truck in question is a 1994 Chevrolet C1500 W/T with the 4.3L V6 engine. Its factory alternator gave up the ghost...it would charge at highway speed or with the engine revved up but never at idle. The battery is not quite a year old, and it tested good at the time.
I put a remanufactured alternator on there and for the first few weeks, things were fine. Just last night, however, the alternator not only stopped charging, but also appeared to be putting a heavy load on the electrical system. The voltage gauge dropped into the red and the lights got very dim. Fortunately, it never quit running.
Upon getting it home, I discovered that the alternator appears to work fine at idle. Rev it up and charging falters or stops entirely. The battery still seems to be in excellent shape (all cells test fully charged with a specific gravity tester even after letting the truck rest overnight), so I suspect the new alternator has gone bad as well.
Any thoughts? I've never seen one fail like that before.