As long as we are doing Chevy truck questions on this group <G>,

I just disassembled the alternator on #2 Suburban, and found that the
magic smoke has indeed escaped., and took most of the insulation off
the stator coils in the process. I HATE it when that happens! So I
removed the regualtor and brush-holder and re-installed it so that it
at least can serve as a belt idler.

On the way up here to the rig, the voltmeter would read normal for a
while, and then slowly creep up to about 18 volts, at which point I'd
kick in the heater fan, etc. in an effort to absorb some of the excess
current. Helped a bit. Then it would suddenly drop down to 12.6 volts
(normal battery voltage) for a while, and then start slowly creeping
up again. Alternator belt not loose; I checked that. No shorts in the
harness that I know of.

This is a Diesel Suburban, but I don't think the glow plug controller
is at fault. It appears to work OK, and the glow plug lamp never came
on while this nonsense was occurring. Had the glow plugs been turned
on that much, I expect they'd have mostly been burned out, yet the
truck starts just great.

I'm inclined to think that it was just a defective regulator in the
alternator that caused all the grief, but it occurred to me to post
this, just in case someone else experienced a similar problem and
found an unexpected cause. This is a very standard 78 amp GM
internally-regulated alternator.

I can get a new alternator easily enough, and there is enough juice in
the batteries to get me a long way down the road yet (two brand new
batteries).

I guess I will install a replacement alternator, and if I see so much
as one instance of the voltmeter reading abnormally, stop and unplug
the alternator harness plug to save the replacement from being smoked.

Gord Richmond