1940 Generator Wiring Question

[MGG]

My 1940 truck manual has a picture of the generator showing only one terminal on the left side that the field wire attaches to. The generator I took off of the truck, (probably a later model) has another terminal, also on the left side, below the field terminal. When I removed the generator this lower terminal had no wire attached to it, yet I think the system charged correctly the last time the engine ran about 30 years ago. Both generators have the armature connection on the back end plate. A 1946 truck generating circuit diagram shows a ground wire from this lower terminal back to the voltage regulator body.
What is different about this later generator from the original 1940 one that it needs a separate ground? I thought that the generators grounded through their mounting to the intake manifold like it does on my 1934. Thanks

[Bruce Lancaster]

the later generator has a stud for a ground wire running to the metal base of the voltage regulator.

The early grounds through the metal parts of engine and body, likely introducing some resistance and loss of efficiency as the electricity goes through dirt and paint along the way. Better charging versus originality...

[Terry,OH]

The original generator did not have a ground wire terminal. In 41 and later the terminal was added. The ground terminal is not necessary but it can help ground the generator body if the V belt adjustment bolt or the front of the intake manifold is dirty or rusty.

[JSeery]

The ground wire goes to the regulator case ground to assure a common ground. It didn't take Ford long to determine the additional ground improved the charging system performance. Unless you are striving for a totally original look on a 40, I would add the ground. You can also add a ground to the one side stud generator buy just running a ground wire from the generator case to the regulator case ground.

[MGG]

Thanks guys - I am not concerned with originality so I am going to add the ground wire. What gauge wire should it be? Does it have to be grounded to the regulator case or, can I just run it straight down from the generator to an intake manifold bolt?

[JSeery]

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The idea is for them to both have a common ground. You could ground it to anything, but the best is to the regulator case. Ford didn't run the extra wire length just for the fun of it, they were trying a accomplish a good common ground for the charging system. The original was a #12.