I conducted research on the subject and found the following things.
Originally, early Delco systems used positive grounding. That’s clear.
It’s also clear that something happened between 5th February, 1942 (production of the last pre-war Cadillac vehicle) and 7th October, 1945 (production of the first post-war Cadillac vehicle) - apart from the World War II. and the things mentioned above:
After 20 years of Ernest W. Seaholm chief engineer era,
John „Jack” F. Gordon became chief engineer of Cadillac in June 1943. In June 1946 John „Jack” F. Gordon became general manager of Cadillac, so Edward N. Cole became chief engineer then.
It means that even if Edward N. Cole had been obsessed with an idea of negative ground, it was too late for him to become the person to change the system, because he got the chief engineer post more than half a year later than the first post-war Cadillac was built.
However,
John „Jack” F. Gordon could be the person, who insisted upon the negative ground system (for whatever reason) because he became the chief engineer between 5th February, 1942 and 7th October, 1945.Anyway, it’s a fact that the only member of GM family using positive ground before the WWII was Cadillac. It seems that this time GM’s other brands forced “Standard of the World” to follow the main line.
If military standards had been the reason for the change then Ford and Chrysler (manufacturers of M3 and M4 tank engines and tanks) would also have changed to negative ground after WWII…..but they did not.
Anyway, let’s see another possible way:
I was searching for authentic sources on the internet for a long time, then I found a homepage which lists detailed technical data of American military vehicles (
http://afvdb.50megs.com) – unfortunately there was no reference for the grounding.
Then I sent an e-mail to Chris Conners (moderator of this website), who sent me the photocopies attached (battery wiring diagrams from TM 9-729 for the light tank M24, published in February 1951). He also advised me to contact the „14th Armored Re-Creations” (
http://www.14tharmoredre-creations.com/). They restored a couple of M5A1 tanks.
Tim Garrett (from the „14th Armored Re-Creations”) answered the following interesting things:
“Regarding your issues on positive and negative grounds in tanks-
The manual shows negative ground in all applications. That being said we have encountered many tanks that were set up with positive ground. Most of the Stuarts in Europe are being operated with pos ground. It works either way but POS is supposed to be hot and NEG is supposed to be ground.
In my opinion POS ground is bad and when we find a euro tank wired backwards we restore it to the manual specs.
The Stuarts were all 12v. The points were extra duty and there's nothing inline to lower the voltage to the ignition. The starters on the tanks have a double solenoid that's routed through the generator. If the generator isn't right the tank won't start (very hard to troubleshoot). Between the odd starter wiring and the gear set up in the started itself they'll work fine either way. The car starter is different and I've never tried to POS ground one. We've done a lot of swaps from POS to NEG ground. Discharge the batt (not necessary but an old timer told me to). Reverse the cables, charge the batt (slow), re-polarize both generators (Bat to field I think- I know what the two terminals look like). Fire it up and it's done.
If you don't re-polarize the gen you're headed for trouble.
There's a really odd design feature on the Stuarts that would make one think they were originally going to be positive ground but the plans must have changed. The odd feature remained. The HOT battery cable is completely uninsulated between the battery and it's junction even though it's really close to all kinds of metal where it could short easily.”
It is like a border of two nations: pre-war: positive, post war: negative, no man’s land: a kind of mixture of both nations but not one particular.
