Pos. ground,Neg. ground. Does it matter???

[pokyjoe48]

The other day my friend and I went and picked up a Model A p/u to service it for a friend of ours for the coming year. The owner is at a point in life were he can't do the work anymore. Well I Thought that A's have Pos. ground. This p/u started and runs with neg. ground. ????? What the... Is there any damage that this can do? This p/u apparently has had Neg. grounding for many years. The thing that caught our eye when we started the car was the amp meter in the dash was reading Negative. We looked at the battery and thats when we noticed the Neg. ground. We rehooked the battery so it now has Pos. ground. Starts and runs fine and the amp meter is on the plus side. Makes my head hurt...LOL

[Sparky]

The car will run fine either way as long as the generator (or alternator if it has one) is correct for the battery polarity. I believe generators can be re-polarized (maybe someone with more experience can add to this.) Alternators may be damaged if the polarity is reversed. Check this as soon as you can.

The only other thing to check, besides the ammeter, is the coil polarity. It will work either way, but it is meant to have specific plus and minus connections.

Fun fact, the starter turns the same direction no matter the polarity!

[newshirt]

Polarity does not matter. It will run fine either way, as you discovered. It's your choice.

But positive ground is the stock configuration, and keeping it that way may ease the minds of future owners decades from now. It's one less "gotcha" they'll have to deal with. Just a thought...

[fiddlybits]

been there....
Sparky has it pegged

There are only two items to check if stock.

1. polarize the generator. (and verify that the cutout has not been blown out)

2. Coil polarity.

There are plenty of threads on all of this but basically you bypass the cutout for a second or two and the generator is polarized.

If the ammeter is showing reverse this is probably all you have to do. The coil is probably still set up for positive ground. The only question remaining is whether the cutout was damaged. If you show a charge when running and no discharge when stopped you are good to go.

[Purdy Swoft]

I use to run model A generators negative ground when I was a teenager. They need to be repolarized to run negative ground. They would sometimes revert back to positive and quit charging. Uncle Coot would touch a short wire from one terminal to the other on the cutout to repolarize. He never told me what he was actually doing. If he did, I couldn't understand what he said when he tried to talk with a cigar between his teeth. Anyway, I finally figured it out. Just because the ammeter registers charge doesn't necessarily mean that it is actually charging. With the engine running at enough speed to charge, you can briefly remove the ground cable from the battery post and if it quits running, the generator isn't charging. Do this very briefly and never do it with an alternator or it will be damaged. If its not charging after this brief test, the generator will have to be repolarized like uncle Coot did. Most of the ammeters that are sold for model A use are actually 26-27 model T and the wires will have to be reversed to register a charge. When changing polarity the wires need to be reversed at the ammeter and the coil. The coil will function either way but spark won't be as hot if the coil is connected wrong. The red wire should connect to the plus side of the coil for original positive ground. If you run negative ground the red wire should connect to the minus side of the coil . The red wire connects to the coil on one end and the ignition switch on the other end. The cutout won't be damaged either way if it is actually a cutout. If it is a can style regulator or has a diode installed in place of the cutout points damage will probably happen when polarity is reversed.

[Mike V. Florida]

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As sparky states, no difference if every thing is hooked up for the ground you are using.

[Willie Krash]

It may be worth a note that if the generator isn't the same polarity as the car it will be in series with the battery.
Early regulators and as far as I know cutouts (reverse current relay) used different metal on the points. This was to equalize wear and avoid pitting.

Now for the can of worms and I will not defend it nor try, in the recent trade magazine for rebuilders they attempted to answer the age old question...pos/neg ground.
They explained that all coils are positive ground (secondary) regardless of the battery and that spark plugs are built for pos ground..!
I'm still thinkin on this..

[marc hildebrant]

One of my books on radio's from the early 1930's recommends that positive ground cars (Model A) should be re-connected for negative ground in order to have the car radio's work best. This has to do with RF noise.

Marc

[RonC]

Jump the cutout terminals with a pair of plier handles to polarize the generator.

[PeteCruz2715]

I bought a 1928 Roadster that had been in storage for a while. The owner was too old to work on the car and so had his "mechanic" friend prep it for sale. I didn't notice at first that the ammeter would discharge when the engine revved. Anyway the battery discharged after a few days so I thought, "well it is just old so a new one is probably in order anyway." As I was replacing the old one I realized the battery had been installed with the negative lead to ground. I thought the car must have been switched to negative ground at some point since the car started and ran. After a few days the new battery was so dead it would not accept a charge. I bought yet another new battery and switched the cables to positive ground and haven't had any problems since. However I was curious as to what other issues may occur due to switching the polarity. After some research I found that the switch in polarity whether from a change in batt cables or a change at the coil will cause the spark to jump from the outboard sparkplug electrode to the inboard electode instead of vice versa. Apparently this leads to a much weaker spark and thus reduced performance. There is a tool you can buy to check the polarity at the distributor. I'd suggest getting one and checking if you are worried about the possibility of a "polarity" issue. Part #17140 - The part goes for roughly $24

[Sparky]

Just unscrew the spark plugs and install them the other way 'round.

[ian Simpson]

Maybe an old wives' tale, but I was told many years ago that switching to negative ground was a bad thing as it caused more corrosion on battery terminals.

[steve s]

As long as we're resurrecting old threads, I might as well resurrect a blurb I wrote a while back for our club newsletter and which I'm pretty sure I've used on a few earlier Ford Barn "negative ground" threads. Don't know how I missed this one.

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.

Steve Schullery

[Tom Endy]

Like everyone has said, negative - positive does not matter. All the electrical loads on the car don't care which way current runs through them, lights, starter, ahooguh horn don't care, they work the same

There are three things on a Model A that are polarity sensitive. The ammeter as you discovered. Easily remedied, switch the two leads to it. The ignition coil, same drill switch the primary leads around. The car will run either way the coil is polarized, but runs a little better when correct. The generator or alternator. The output of either should match the battery polarity. If the car has a diode installed in the cut-out switch in place of contacts, add a fourth thing that is polarity sensitive.

Tom Endy

[w.michael]

OK, my first dumb question of the day. (More dumb questions will probably follow.) When you jump the terminals to polarize the generator, do you do it with the engine running or off?

W. Michael

[Tom Wesenberg]

Originally Posted by w.michael

OK, my first dumb question of the day. (More dumb questions will probably follow.) When you jump the terminals to polarize the generator, do you do it with the engine running or off?

W. Michael

Off, you want the correct polarity before you start the generator spinning.

[rollingsculpture]

Originally Posted by Willie Krash

It may be worth a note that if the generator isn't the same polarity as the car it will be in series with the battery.
Early regulators and as far as I know cutouts (reverse current relay) used different metal on the points. This was to equalize wear and avoid pitting.

Now for the can of worms and I will not defend it nor try, in the recent trade magazine for rebuilders they attempted to answer the age old question...pos/neg ground.
They explained that all coils are positive ground (secondary) regardless of the battery and that spark plugs are built for pos ground..!
I'm still thinkin on this..

its the direction of the spark tip to base

[roccaas]

Question, does Ohm's Law change in any real way if a circuit is positive ground versus negative ground?

"V/I=Futile" ~~~ this is posted as a 'signature' of an Electrical Engineer on a Georgia Tech sports website I visit almost as often as I visit FB!


2+2 approaches 5 for all large values of 2!

[Sparky]

Originally Posted by roccaas

Question, does Ohm's Law change in any real way if a circuit is positive ground versus negative ground?

Nope, not in the slightest.

[Napa Skip]

Originally Posted by roccaas

Question, does Ohm's Law change in any real way if a circuit is positive ground versus negative ground?

Fortunately, whether it's electron flow or hole flow, electrical laws (Ohm's, Coulomb's, Kirchoff's, Oersted's, etc.) - even Archie's Law (electrical conductivity of certain types of rocks) - hold, regardless of ground polarity (and even in ungrounded - e.g., shipboard - electrical systems).

Perhaps you hadn't noticed the grounding strap on rocks...

Zaaaaappppp!!!!