The Stovebolt Site Forums The Shop Area The Electrical Bay Another 1946 Chev - GMC regulator question

I am comparing the wiring between a 46 GMC and 46 Chev I have and note a difference. The wiring on the GMC has 3 wires for the generator, whereas the Chev. only has two. Can someone explain what the difference means? Both the trucks, I am looking at, are 1.5 ton trucks. Could someone share a wiring diagram of a 1946 GMC with me?

Alan,

I'll guess that the extra GMC wire is a ground wire to a machine-screw into the generator case/body?

Running a ground wire between the generator housing and the regulator base usually makes the regulator operation more reliable. It's a good idea on any vehicle, as otherwise the ground for the regulator control circuit has to rely on a convoluted path from the body to the frame, then back to the engine. You will probably find a wire going to the regulator base that will be the other end of the one attached to the generator housing. Check it with an ohmmeter with both ends of the wire disconnected. It should read zero ohms or very close.

Here's a generic wiring diagram from Delco for all GM generator/regulator circuits with the "A" design, where the ground for the field coils is found at the regulator. That covers virtually all GM vehicles I'm aware of.

http://www.hunt101.com/data/500/D-R_Regulator_001.jpg

Jerry

Yes, I think that ground wire on my 54/55 6v GMC runs from the generator to a base screw for the voltage regulator (or more likely to a screw nearby the voltage regulator).

My GMC is 550 miles from me - but, I think the voltage regulator is isolated from the firewall with heavy rubber grommets that the attachment screws go through?

The vibration isolators are there, but one of them also has an integral jumper that allows the attaching bolt to get a ground. They're notorious for getting a little rust or corrosion at that connection. Then the regulator can't function properly. The ground wire was usually attached directly to the regulator base with a small sheet metal screw if one was used.
Jerry

Thanks to you fellows for your quick response and help as I tried and was successful in putting my dump truck into service today. I wired up the generator, as was suggested, but didn't take the time to actually check the nasty old generator I am using for its output. I did run the truck for a couple of hours straight hauling some sunshine to the sweet corn patch. So far so good.....
http://s209.photobucket.com/user/al...C01141%20800x600.jpg.html?sort=3&o=0

It's good to see an old rig actually working instead of being somebody's Cowboy Cadillac! My grandparents bought a new dump truck back in the late 1930's when Sewart Air Force base in Smyrna Tennessee was being built, and hired two drivers. They ran the truck 24/7 for several months, hauling gravel for the 4-foot deep base for the 2-mile long runway. The drivers worked 12-hour shifts and the only time the truck stopped was for routine maintenance, gas and oil. I don't know what make the truck was, but at the same time they were hauling beer from Milwaukee and St. Louis to Nashville with a pair of 34 Chevy tractor-trailers. The trucks had vacuum boosted mechanical brakes, and the trailers had no brakes at all!
Jerry

The old and bad looking generator I used in order to haul cow crap is not working. I suppose I could rebuild this one, but frankly, the cooling sheave doesn't look very good and the case looks worse. I would sooner start with a better generator to rebuild. I did have enough battery to haul for 7 or 8 hours and actually accomplished something.