The Stovebolt Site Forums The Shop Area The Electrical Bay 1939 GMC positive or negative ground

Slow down a bit Jack. First things first. We can't start helping you before we know what parts you have and your goal.
1. IMO Change to negative ground. very easy
2. IMO Change to 12V system.
3. Post picture or part number of the alternator you have.
4. Do you have a voltage regulator?
5. Do you have a ballast resistor?
6. Do you have a foot start starter? Is it 6V or 12V?
7. What motor is in truck?
8. Early GMC's having positive ground is a well known fact around here. They went to neg in early 50's.

It seems to me you are between making up your mind on 12V or 6V....and Neg or Pos ground and have some kind of "alternator" not generator.
So need to get it all sorted out, then we will help hook it all up. I do recommend 12V negative ground and using a Delco 10si alternator. Many have gone this route and we have helped them do it.

The grinder is for later. You can continue to start by hand. As Bill says the winding with a capacitor in series will magnetize slightly earlier than the winding without the capacitor. The old single phase motor on it should have been wired to start in the correct direction. And yes switching wires will casue motors to change direction.