Ford CMP Voltage Regulators

[BCA]

The wiring schematic in MB-F1 shows the battery as having a positive ground. Various Ford parts books show a choice of a voltage regulators with either positive ground (regulator C11A-1505) or a negative ground (regulator C11AS-1505).
I can't see any discussion in the manuals about the regulators being either positive or negative ground. Why were there these variations.
If your ammeter reads backwards then it would indicate you have chosen the wrong battery terminal as your ground.
Can anyone clarify this issue.
.... Brian

[Tony Smith]

Brian, you need to re-check your parts stock! The basic Ford number for voltage regulators is 10505, not 1505.

These were a common part across many Ford vehicles, and not simply restricted to CMPs or even military vehicles. In the CMP parts lists, there are an amazing 9 variations of these regulators listed, with differences being for:
1. Pos or Neg earth,
2. Battery Specific Gravity (a new concept to me, I thought all batteries ran the same spec grav for "charged" or "discharged" state!), and
3. Country of manufacture.

I have in my possesion a "Made in USA" reg, a "Made in Canada" and an ENFO "Made in England". Only the English one appears slightly different (and that may be because it is possibly Post-War manufacture), yet the mount holes are identically spaced and will interchange with the North American versions. It is not listed in the CMP Spare Parts Lists, but I also have references to a 35amp regulator and a 50amp version.

Why the option of Pos or Neg earth? As stated above, these were a common item across many Ford models, for export to many countries. Even the "Standardised" CMPs were specified differently for particular contracts to certain buyers. I would presume the contracts for supply to Britain and possibly India would have followed national preference/practice at that time for Pos Earth vehicles for compatibility with existing fleets, while contracts for supply to Canada would have followed North American preference/practice for Neg Earth. On Australian Blitzes, I have seen both Pos and Neg earth systems, so our stock of CMPs would have come through a variety of supply contracts.

[cletrac (RIP)]

Pretty near all Canadian 6 volt systems are positive ground and 12 volt systems are negative ground. There are exceptions of course but not many.

[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

[Lynn Eades]

It is a matter of "polarising" the field magnets (they screw into the case and suport the field windings. This is done simply by hooking a wire from the live terminal of the battery and striking it to the field (small)terminal of the generator.
You ammeters in your Dodges can be fixed by simply swaping the wires on th back from one side to the other.
The "polarisation of the fields is important, because if its not done, the geny starts charging, the points(contacts) close, and when you stop the motor, they stay shut. the geny tries to "motor" but is held from doing so by the belt, and it cooks up your regulator and generator.