Generator Light on - 59 GMC 1/2 ton w V8

[bevman]

I have a "new" (rebuilt) generator and a new regulator and the red gen light is on. Goes off when idling, but comes on about half-strength when driving. New belt has 3/8" of deflection. I took it to my mechanic and he said that I needed a new regulator so I got one. I did spark the regulator with a jumper wire, as directed, to polarize.That didn't fix the problem. This started just after I had the engine pulled to replace an undersized piston (long story). Any ideas? - Michael

[mr48chev]

It almost sounds like it is working backwards as most of the time with a generator the light might come on at an idle when the generator isn't putting much out and the then go out when the engine speeds up.

First, what does your hand held volt meter say as far as charging when the engine is running and when you speed it up? You might not get 14.2 but you should get 13.8 to 14.8 volts with the engine revved up a 1340 rpm for 30 amp and 1840 for 40 amp and up generators . Lots of specs here with the generator specs being on paper page 21 https://www.gmheritagecenter.com/doc...olet-Truck.pdf

[bevman]

Which post on the generator is the "hot" one?

[Coupeguy2001]

Go to the regulator and clip on the "bat" lead.
When the generator is producing, you will get about 14.2-14.4 volts.
When the current cut out turns off the generator, the battery volts will slowly go down maybe 3/4 volt. Use that terminal for your measurements.

On my old Gen, there was a G terminal and an F terminal. On another gen, the G was an A.

A or G is output.
F terminal is field.
What you can do, for about 2 seconds, you can ground the F terminal, and that will make the generator put out maximum volts and amps.
Have the meter on the bat terminal on the regulator to see what it puts out.
only 2 seconds though, or you burn up the generator.
Had a shorted field coil once, and had to turn everything on to keep from burning up the generator on the way home from work.
turns out, I had to throw it away anyway.
Once, I had a bad condenser on the generator, and it exploded and then everything was normal.
Just a generator whine in the radio till I got another one..

[bevman]

Thanks for the help. I'll give it a try.
Cheers!
Michael