Ford CMP Voltage Regulators

[Phil Waterman]

Hi All

Is the Positive 6 volt Ground a Ford thing?

All the Chevy trucks of the prewar and war years that had 6 volt systems with Negative Ground, I've encountered . My copy of 1940 Shop Manual for Passenger Cars and Trucks for General Motor of Canada shows on the wiring diagram Negative Ground for both on the car wiring diagram and truck wiring diagram.

Checking my MB-C1 and MB-C2 both show Negative Ground

What have other people found?

Cheers Phil

[Grant Bowker]

Most (all?) GMC trucks of that era were positive ground, with Chevrolet being negative. I have no idea why General Motors did their two truck brands differently.

[Mike K]

I believe the early Dodge 1/2 ton WC series were positive ground 6 Volt . Gordon will know more .

There were NOS Ford regulators around . I had one .You have to clean the contacts before use , they tend to oxidise . Mike

[Stew Robertson]

I believe that it was a Engish Gov`t requirement that prompted the positive ground thing from the Canadian manufacturers If memory still serves me this issue was brought up at the seminar in 84
But it never became fully implemented and that was why the variations
BUT I COULD BE WRONG AGAIN! Memory is a funny thing

[BCA]

Thanks for the comments, in particular to Tony for correcting the part number. My NOS positive ground voltage regulator has no markings or data plate to suggest the polarity - the only indication is from the packaging which gives the part number for positive ground model.
If you have an unmolested truck then the best indication of the original grounding would be from the holes sizes of the battery cable terminals.

Dodges: Both of my American 1/2-ton WC Dodges are missing the original battery cables so I follow the modern convention of using a negative ground: while the electrical systems charge OK, the ammeters read backwards indicating that they originally had positive grounding.
... Brian

[Ken Hughes]

Brian there is a way to change the polarity by holding down one of the contacts inside the regulator,i dont remember which one??,but you hold it down for an instant with motor running and it reverses the polarity,maybe some one can remember excactly?

[BCA]

I believe the polarization procedure has to do with the generator, rather than the voltage regulator.
... Brian