MTFCA Forum

A friend just bought a nice '24 T runabout, and older restoration. The battery is connected for negative ground! It seems to charge and work OK. Does anyone know why this might have been done? How can we change the generator and/or cutout to bring it back to positive ground?

Negative ground is correct.

Negative ground is correct for the Model T.

Change nothing, Model T's are Neg ground, Model A's are Pos ground.

The Real question is WHY?

That has never been explained!

You can flash the field and reverse the generator output anyway, if needed.

That is done by jumping around the cutout with a short wire for a few seconds with the engine running at a fast idle.

I don't know why. They seem to work equally well. Ts are negative ground, and 1928 through 1955 Fords are 6 volt positive ground.
Mopar and Packards were positive ground for many decades. GM seemed to be all negative ground. Studebaker? Hudson?

Educate yourself. These are a must for T owners.

Negative ground

Hi Martin
Reading your post you seemed surprised that your friends T is negative ground. Your profile shows you have a 15 Runabout and if it’s a stock T it should be negative ground also or has it been changed to positive ground.
And as others have stated Model T’s are negative ground and work fine that way. I’ve owned the newer Fords and other makes with positive ground but never questioned the reason why they were that way since they worked fine for me. Just my opinion!!

For reasons evidently known only to Ford Motor Co they changed to Positive ground when the Model A came out as 1928 models and stayed with the positive ground thru 1955, then changed to 12 volt, negative ground, I think.

And now this:Positive vs Negative ground. Is there an engineering reason? (circa 2022 discussion)
https://forums.aaca.org/topic/388502-po ... ng-reason/

“Positive ground causes nuts and bolts to vibrate clockwise”… and… “negative ground causes nuts and bolts to vibrate counter clockwise”. Are you kidding Dan ? Thats akin to stating toilet water flushes in different directions in Northern and Southern Hemispheres

I read once that Ford changed to positive ground on model A's so they could be sold in Europe. European cars weren't allowed to be sold if negative ground.

Of course Dan was kidding.
Conventional theory says that electricity (Electrons) flow positive to negative, and that's the way we generally think about it. Electron theory says just the opposite - Electrons flow from negative to positive. Obviously we are talking DC current. An Electron can be defined as a negatively charged sub-atomic particle. Why is the negative terminal of the battery negative? The answer is that's where the electrons are. The protons are hanging out at the positive battery terminal. Electrons are attracted to protons, so the reality is that Positive ground is wiring things the way the electrons actually flow. That is counter-intuitive, so modern (and some older) cars and trucks are wired negative ground.

Once a coil fires, the secondary current is AC, not DC, so I don't think system polarity would matter to spark plugs. Coil PRIMARY polarity is important.

""Once a coil fires, the secondary current is AC, not DC, so I don't think system polarity would matter to spark plugs. Coil PRIMARY polarity is important.""



The vibration and shaking of a model T is the result of the Alternating Current of the magneto.

When a Model T is operating on magneto among a herd of cows, the cows will cluster around it due to the magnetic lines of force emanating from the magneto and coil box.

The vibration is much worse on magneto due to the rapid tightening and loosening of all the steel nuts and bolts on the car due to the rapidly reversing polarity of the magnetic field.

And avoid T’s operating on MAG if you have any piercings!

Maybe he knows??,!

This thread has gone from helpful to bizaare.

Oh dear - the thread has become shocking to some reading the comments.

Readers should maintain a positive attitude. Current posts have sparked some informative feedback and a battery of questions. The short of it is negative comments just lead to polarizing this friendly forum.

(Scott - the cows think they're going to be fed )

I agree Rich B., it’s all about how we Conduct ourselves!

Corrosion occurs on the positive side. Ground conductor s are cheaper and easier to change. Hence; the ground has been positive in the past.

Then, a few years ago diodes were given me a problem when upgrading the generator cutouts.

My cutouts I made for a Model T were always correct for a Model A.

Then, I learned that in the early years, the arrow on the diode represented hole flow and the current flow went opposite the arrow.

Now the current flow goes with the diode most of the time, but you have to read the diode specification sheet to know which direction is correct.

The best likely reason was this one found on the AACA Forum!

Why Negative Ground?

A recent forum discussion thread on the Fordbarn.com web site motivated me to go back and look again at an article in the Skinned Knuckles magazine. The article, "Why Negative Ground?" was in the September 2009 issue, #398. The simple question about a relatively modern occurrence was asked by a reader: Why did all remaining positive-ground U.S. manufacturers switch to negative-ground in 1956? After extensive research seeking an answer, the frustrated editor concludes,

"Much as I would like to announce that we have an answer, unfortunately just the opposite is true. Not only have I not obtained facts, but I am also puzzled beyond belief that the wide variety of automotive historians and curators whom I questioned could not come with a factual answer."

One U.K. electrical engineer and museum curator who was queried on the subject replied, "You have opened a can of worms..."

The SK article includes a table showing ground usage by 35 car models since 1932. Twenty five of those used positive ground for at least part of their existence. The various models that became part of GM, except for Cadillac, always used negative ground, as did Duesenberg, Essex, Stutz, and Reo. Cadillac switched from positive to negative ground after WWII. Hudson switched from negative to positive ground in 1934, and then back to negative in 1956. The "universal" switch to negative ground never occurred in the U.K. Nash Metropolitans remained positive ground, and allegedly some US car models made for export to the U.K. are still set up with positive ground.

The various creative, speculative or bogus rationales supporting one or the other grounding usage that have been offered over the years, including the corrosion thing, are briefly reviewed. The fact is that in 1956 there was a sudden consensus that it would be a good idea to standardize, but exactly how and why that consensus emerged at that moment in time remains puzzlingly mysterious.

I think it's clear that there really is no strong argument to be made one way or the other, but standardization is a good idea, and, happily, it came to pass! Too bad Ford was on the wrong side of history, but it's no big deal.

All Nash Metropolitans were assembled in England and were positive ground.

My 1915 runabout is 6 volt positive ground. Of course the chassis had no polarity when the car was built, T's didn't have batteries until 1919. Whoever installed a later engine/starter/generator in my car years ago apparently decided to make it positive ground.
This is my first T - I assumed all T's were positive ground. I may change it to negative ground now that I know that's the standard for T's.

My 15 touring of course has no battery electrics except for the one powering the stoplight and coils... I have it rigged so I can run either positive OR negative ground to avoid undue depositing on the coils points... not that I ran the car much off battery... maybe I was just being over, um, retentitive about it... But unless you're running FA starting & lighting equipment on your car, it shouldn't make a dif. If you are, of course, then it does.

And I won't mention those funny looking things people attach to their engines using a single, round coil (like those "C" word cars do....)

Didja ever think how far ahead Henry was thinking? He was not using a distributor and had multiple spark coils - then the industry switched to a single coil and distributor. Now the distributor is gone and modern cars have multiple coils. The model T had tall wheels with high-pressure tires that had relatively short sidewalls. As the years progressed, the wheels got shorter until they finally reached 13 inches and fairly tall sidewalls for some of the smaller cars. Now the wheels have gotten much larger in diameter and the tire sidewalls have gotten much smaller. What goes around comes around. BTW: I forgot to mention that we have also returned to non-standard headlights. Perhaps our Ts were more advanced then we thought.