It is your alternator. It appears that the voltage regulator slip rings were improperly installed on a bunch of the 3g alternators. The slip rings are what the carbon brushes ride against on the rotor. What happens is the carbon dust from the brushes builds up and creates an electrical path to ground across the the melamine insulating material. This can result in a High or Low voltage condition and usually occurs when the vehicle(engine) is under load.
The fix is rather easy. Remove the alternator. Remove the voltage regulator. Mark the case for alignment/clock position. Remove 3 long/small diameter bolts holding case together. Look at the slip rings(one assembly). They are probably touching some of that gooey crap. Use a tool to seperate the slip ring from this stuff. Sliding the slip ring down the shaft a little is allowed just observe where the brushes were wearing and don't go to far. Next dip the rotor in a bucket of water to rinse off the carbon. Repeat this several times. Let rotor dry/blow dry and reassemble. Use a paper clip or similar device to pin the brushes back up in the regulator for reassembly.
Why this has not made a recall yet baffles me. Does anyone know of a TSB on this? The alternator on my 90 came from a 95 and was spiking high. The auto electric shops I took it to said "It tests ok!" but the rotor windings were grounded. Amazing, none of them even tested it to see if it was grounded.
Oh yeah, this problem doesn't get fixed in a typical rebuild. The slip ring must be moved to fix this problem. I received a 3g rebuild for a customer and it was screwed up the same way.
Mike
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[This message has been edited by moosejaw (edited 08-29-2001).]