Positive vs negative ground

nhusa

nhusa

Well-known member
I know that Model As are positive ground but have heard that they can be converted to negative ground.

How is this done and what are the advantages and disadvantages of doing this?
 
It depends on whether you want the electrons to move from front to back or back to front.
 
Here's something I wrote up a few years ago for Ford Barn and our club's newsletter:


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
 
There have been lots of articles published about why,but I've never seen any real reason except that was what they chose to do at the time.I just see no reason to convert.It is a simple enough matter to do,change the wires on the battery,coil,and ammeter.A change to a diode cutout makes it nice too.Years ago I worked on a Mack with positive ground that had a new sander in the back.It had a Briggs pony engine to run it,but it would eat stators,and the small engine guys had no clue as to why.The little light went on in our heads when we saw the dash lights glowing with the truck engine off and the sander engine running.The sander engine was a self contained power plant with it's own battery,and was negative ground.The old electric shop guy we used at the time said it shouldn't matter,but he did a lot of hemming,hawing,and wouldn't give a straight answer.He did tell us that theory is one thing,but in real life we should isolate the power unit from the truck.
 
In the early 70's I worked for Montgomery Wards (Monkey Wards) in their tire and battery department. Being inexperienced, young and stupid, I had an old Nash come in one day (Don't see them about much these days, for sure). Any rate, I hooked up a new battery to it completely backwards, as I was not familiar and had zero training as to what I was doing at the time. No arc, spark or noise at all and the customer drove away happy as a lark to have his new battery installed. No one checked my work before the car left the work bay.

The next day when I arrived at work, I got a very thorough fanny chewing from my boss as the customer had returned later that evening with his car in tow and Ward's management agreed to pay the damage and the towing expense for my stupid mistake. Believe it or not, they didn't fire me and I guess I'll never know just why (probably because of my good looks). Like say, I was a kid at the time and I had no clue as to negative or positive ground differences on any car, let alone one with some age to it. I just remember that I had a bit of trouble in getting the lead end piece of the battery cable to fit correctly onto one of those poles and had to force one. Maybe that should have been a clue that I was doing it wrong, huh? :-)

I sort of chuckle a bit at this thread, as I always see similar ones in the archived threads here and someone always seems to post the same diagram to show the wiring for a Model A. However, that wiring diagram is for a 6v, positive ground and not the 12v negative one. Surely there is also a 12v diagram to be shared. :-) My '30 ccpu came with the 12v conversion done by the previous owner.
 
coupe1942 said:
...

I sort of chuckle a bit at this thread, as I always see similar ones in the archived threads here and someone always seems to post the same diagram to show the wiring for a Model A. However, that wiring diagram is for a 6v, positive ground and not the 12v negative one. Surely there is also a 12v diagram to be shared. :-) My '30 ccpu came with the 12v conversion done by the previous owner.
Click to expand...

Whenever someone changes from 6v+ to 12v-, all bets are off as to what the wiring diagram is or should be. Most often there are other changes that have been made along the way.

When I got my 12v alternator, it had a simple wiring diagram to affect that change. Changing from a pop-out switch came with another change. Adding turn signals came with another change. And so on and so on.
 
Back in the stone age when I was trained in electronics by Uncle Sam, we were taught that electron flow was from positive to negative, perhaps that's why they decided in the day to do it that way.:confused:
 
Jemelton# said:
Back in the stone age when I was trained in electronics by Uncle Sam, we were taught that electron flow was from positive to negative, perhaps that's why they decided in the day to do it that way.:confused:
Click to expand...

Even that is only partly true. It depends on which part of the circuit you are looking at - the wiring or in the battery. This is from a govt website:

Electrons are negatively charged, and so are attracted to the positive end of a battery and repelled by the negative end. So when the battery is hooked up to something that lets the electrons flow through it, they flow from negative to positive.

This is INSIDE the battery but in the wired circuit outside the battery, electrons flow in the same direction around the loop and so go from the +ve terminal to the -ve one.
Confused yet? We haven't even begun to look at the flux spectrometer.:D
 
SeaSlugs said:
Good ol hole theory VS electron theory...
Click to expand...
If I remember correctly:
The Air Force taught that the Electrons moved from the negative to the positive.
The Navy taught that the Holes ( or vacancies) moved from the positive to the negative.
 
A solid state conductor with an unbalanced amount of positive & negative electrons, is said to have "holes" in it.
It took me years to get an explanation of HOW & WHY a diode works. I accidentally found it in the encyclopedia, under solid state semi-conductors.
I once had an alternator I couldn't fix---Back to the encyclopedia, under A/C motors & generators & found my answer, I don't recomember whut it was??? BUT my Manager gave me a GOLD STAR!!
Bill Zap
 
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My 50 Ford Coupe amp read backwards when I bought it. Checked the battery and it connected backwards. Every thing but the amp meter worked fine. It was easier to reverse the battery than the amp meter.
 
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