1939 Ford sedan - Question about rear terminal on generator
 

Searching the forums here, I am looking for a diagram of wiring order for 6v generator to voltage regulator for 1939 Ford sedan.

This is my first 6 volt Ford project. This was my fathers car, apparently the owner before converted it to negative ground.

Positive cable goes to solenoid. Ground battery cable goes down to the outside shaft of the starter. But when I drive it around the block with a full battery charge, it stalls out, wont start with a low battery.

I took my generator in to the shop and the tech said it was ok, and that it was negative ground.

There was no connection to the back terminal. What goes to this? Is it ground? Or is the ground next to the Field on the side of generator?



Thank you!

https://i.postimg.cc/prrMxC8f/IMG-1329.jpg

Re: 1939 Ford sedan - Question about rear terminal on generator
 

The rear terminal is the A armature connection. The ground is the terminal marked G in your photo.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

That G wire is going into the firewall under the dash. If it's ground, shouldn't it just ground into the frame?

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Originally, it grounded to the voltage regulator. The early regulators were insulator mounted which required the grounding connection to the generator. The link illustrates an old style regulator with the ground terminal on the left side. Rubber grommets with metal inner bushings were fitted to the mounting lugs for firewall attachment. They are missing from this example.
https://www.ebay.com/itm/402327949163

A lot of the 39 models still had tree brush generators but it depends largely on whether it's a standard or a deluxe model in 1939.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

On a 6v system, your A and G wires need to be 10 ga. While hard to tell from a picture, those look a bit skinny.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

FYI, not that it probably matters to you, but that isn't a '39 generator.
The photo I have attached is a proper '39 generator and although you can't see it, there are but two terminals. One on the rear and one on the side. No ground terminal whatsoever.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Ideally the ground wire should go to one on the screws/bolts mounting the voltage regulator. They do best with a common ground. Need to be sure the ground is actually making contact with the firewall metal as some regulators have rubber mounts.

A couple of diagrams, not 39, but it wires up similar. One diagram is 41-41 and the other is later 49-50. The last one calls out wiring size.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Not per the Ford manuals and wiring diagrams.

A 10g
F 16g
G 12g

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Interesting. My source is the tabulation from 2015 that cited a number of references and did acknowledge discrepancies between them.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Just another nit picky aside here BUT since you are working on the whole shabang....... you might want to change the coloring of two of the wires and get away from having ALL three Red!!!!! ALSO maybe get a soldering gun and heat shrink and ditch those "crimp on"plastic colored shrouds on all those terminal ends too!!!!

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Looks like the same values to me. Except 12g vs 16g on the ground.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

The generator grounds through it's body to the motor. So the G wire isn't doing all the grounding hence it doesn't need to be as heavy as the main armature wire. The ground lead is more of a noise reduction type device so the regulator and generator are at the same potential.
Or something like that. I'm not a trained Sparky.
Mart.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Sharp observation Mart.
In fact, if I may add to your comment, Ford did "mask" the rear of the front generator mount while painting the assembly. Thus, a better ground path.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

If your going to change the wire colors as noted above, ground wires are usually black. Good way of keeping track of grounds.


As the suggestion to change the terminals, I dump the plastic part and usually use black shrink tubing. Looks a lot nicer, almost factory

Re: 1939 Ford sedan - Question about rear terminal on generator
 

^^^or short sections of black rubber tube instead of the plastic.

Nice you are keeping your Fathers car going. I like that. I hope all goes well.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

Interesting that your Ford is running negative ground!! How about the ignition coil - stock? That was designed for a positive ground system. Or did somebody put an adapter on the distributor and connect a can coil? What do you have? The regulator is 6v positive ground or did somebody install a 6v negative ground regulator? I just got done working on my generator and regulator and I had to run a 16 ga ground wire from the generator to the frame of the regulator to get rid of a 0.1 ohm resistance between the generator and the frame of the regulator, which resistance was causing the ammeter to jump all over the place, notwithstanding a braided ground strap between the engine and the firewall with clean connections!! Make sure that you polarize the generator fields by momentarily touching the field wire from the regulator onto the battery terminal on the regulator. My regulator has a frame that is mounted to the firewall - no rubber bushings.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

I reread your initial report wanting to know what the back terminal on the generator connects to - the answer is it connects to the armature terminal on the regulator. My generator would not charge unless I revved the engine and then it was okay. I checked the continuity between the armature and field terminals on the regulator and had zero ohms - ok I removed the generator, removed the backing plate and cleaned the field and armature terminals, and checked the continuity for the grounded brush. I tightened the two terminals for the field and armature - CLEAN AND TIGHT. PROBLEM SOLVED. Your ammeter should give you some idea what is going on.

Re: 1939 Ford sedan - Question about rear terminal on generator
 

To change polarity, all a person has to do is re-polarize the generator field shoes by flashing the field. It should still function either way. Ignition coils that were original to a positive ground system will need to have the connections to the coil terminals reversed in some way. Skip Haney could rework a distributor mount coil to work on negative ground or a can type coil conversion could be used.

Polarity changes will change direction of current flow in the circuit but the electrical components generally don't care about flow direction unless there are solid state radio components in the vehicle or non shunt wound electric motors. These types of electric motors would require the swap of terminal ends to get the proper direction of rotation.

If still running on 6-volts, I'd put it back to positive ground just for the flow advantage if nothing else. Electrons flow from the negative side to the positive side of a DC system. With a 12-volt system the advantage is negligible.