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Anyone know if there was any logic behind Chevy choosing negative ground and GMC positive ground???
Denny Graham
Sandwich, IL

There are all sorts of great stories on this one. Try a search.

The bottom line is that there might not have been a good electrical/physical reason. The electrical system in almost all vehicles is isolated from true "earth"/ground.

From my "Dawn of Time" electronics schools we were told....Electrons have a negative charge. Therefor electron flow or current flow is negative to positive. But in the real world using the number line that we learned in grammer school only positive numbers really exist. In other words, you can't take 2 negative apples and give to Johnnie. To make a complicated idea simple in order to train electronics people quickly in WWI and II and such, they invented "positive logic", where current flow is postive to negitive. Today we call it "hole flow". Little tricks like turning the colors of the voltmeter leads around and reversing the (+) and (-) markings on capacitors, etc. and you got it. It really doesn't matter when doing electrical work on trucks other than we need to ALL be the same page as to what is positive and negative. Hope this helps.

some long time ago, frd said it made for a more efficient ignition because of the direction electrons flowed through the spark plugs. maybe at that time it did make enough difference, but not today.

I was kinda wondering that myself! I do know that my 48 Ford 8N is Positive ground and my 46 Chevy is negative. The Ford tractor runs better Positive ground (yes, I "polarized" the VR). I also have a 1967 BSA motorcycle that was positve ground. It ran better when I switched it to Negative ground.

67 Lightning, wish I still had it, traded it in for tubing for the bi-plane, big mistake the bike was more fun.

Well I haven’t heard any logic that would sway me one way or the other so this is the deduction that I have drawn. If you jump over a puddle from the sidewalk to the street or from the street to the sidewalk it’s the same distance, requires the same amount of energy. If the spark jumps from the electrode to the shell of vise versa it’s the same distance, the same heat is produced. I can’t see where that would make any difference in the ignition of the fuel as the arc is traveling at a speed that is so much faster than the flame front that its of no consequence. Light bulbs light and fans turn and spark jumps the gap equality well no matter what the polarity is.
There are libraries full of books that discus Conventional Current vs Electron Flow. In the end this debate equates to the “chicken or the egg”, “is the glass half full or half empty”, etc. Hole flow in sold state theory is a “hole” different subject. Again when you are talking about a spark gap it makes absolutely no difference in my opinion.
The only thing that makes any sense what so ever in my opinion is that GM wanted to make sure that you had to buy polarity sensitive components for your GMC, from a GMC outlet and the same for the Chevrolet parts.
Denny Graham
Sandwich, IL

The early forties Chevies had a device that changed the polarity of the points each time you started the vehicle to minimize the pitting and peaking of the points. It didn't affect the rest of the electrical system.

Even messier is the fact that DC electrons flow one way and current, by definition, flows the other. Yikes! No wonder chemistry is easier than physics!

Hey Denny, You sound like you know what you're talking about. You might want to check this out. Hole flow may go back further than one would think. http://mste.uiuc.edu/murphy/holeflow/holeflow.hmtl

O.K., so - what does my trusty ammeter measure, electrons or holes or (?)

Amps!
Denny G

Yeah - I still have my BSA 1967 Lightning and a couple Thunderbolts out in the shed. I even have parts of an A10 out there. One thing on them old British machines - they had Lucas Electrics! The old Zenor Diodes, heat sinks and rectifiers. Remember that - in the British Motorcycle world - Lucas was dubbed "The man who INVENTED darkness"!

And the only product "Prince of Darkness" made that didn't suck was a vacuum cleaner.

Grab up some of the old AN electronics manuals from WWII and they were teaching Conventional Current. I went through USAF tech school in the mid 60's and some of the instructors (old timers) were trying to muddy up the works by teaching it.
If the guy at the front of the ticket line gets his ticket and moves on, that leaves a hole for the next guy to fill, so on down the line. So the flow of traffic is of people toward the ticket vendor, the flow of holes is in the opposite direction. When an electron moves from one atom to another that leaves a hole that needs to be filled by the next electron in line. So the way I view it, current flow is electron flow. Many picture electrons racing thru the conductor at the speed of light but in reality they move quite slowly. The energy is transferred much like it is if you were to line up all the pool balls in contact and strike the first one in line. The energy is transferred through all of the balls and the only one you see move is the last one. We’re getting way to deep for a discussion about a spark gap here.
Oh and you Waldo, I'm sure you were just being factious, but if not, since the needle is attached to a coil in a fixed magnetic field that its inductively reacting to the flow of a current of electrons that carry a negative charge. A hole is a void, a void moving through a wire does not create a field, it is only there because the little ol’ lectron has move up to the head of the line.
Denny Graham
Sandwich, IL

Ah yes, Denny my man, I was being a little facitous there. Current flow is indeed electron flow since: 1 Amp = 1 Coulomb of charge per second. And, 1 Coulomb = 6.24X10(to the 18th power) electrons. Without our little friend, the free electron, those ol' ammeters would budge nary a hair.

I agree with Denny. Some of us (or is that me) seem to be trying to show how much or how little we know. Guys are seeking answers to questions to get/keep their rides running and we're talking hole flow. HELL-O, who cares! As the old saying goes..."When you are up to your arse in alligators, it's hard to remember you're here to drain the swamp", or as Jack Webb use to say..."Just the facts Ma'am". I will strive to remain more focused. Thanks Denny.

One more off-topic
I think a positive ground will rust faster?
negative ground helps to slow oxidation by replacing electrons in the chassis.
??????
Maxx

The difference creates a larger 'parts market' in theory. In reality, you just need to "re-polarize" the regulator/generator if using Chevrolet parts on a GMC etc.

It all becomes moot in 1955 when all changed to 12V neg. ground and Yes; motor vehicles are 'isolated' from the earth via the rubber tires unless a "static strap" was installed.

Remember those??

1955 1st-series Chevrolet trucks had 6v negative ground; and, 2nd-series Chevrolet trucks had 12v negative ground.

For some reason, 6v positive ground was still standard on the 1955 6 cylinder GMC trucks. In 1956, all 6 cylinder GMCs were 12v negative ground.

1955 GMC Features
1956 GMC Features

We have some real electrical wizards participating in this thread, so let me ask a "somewhat" related question. I have two Ford diesel tractors (12 V) and used to have a Ferguson diesel. Every few months the engines will not start due to a build-up of a thin, flat black glaze on the positive battery terminal. I remove the positive battery cable, clean the terminal end and the battery post, reattach, and all is well for a few more months. This condition happens with new batteries and cables, as well as old ones, and can occur if the tractor hasn't been started for three months, or if I just shut it off three minutes ago. It is definitely not a loose cable issue, and it never occurs on my gas-powered machinery. I presume it has something to do with the fact that in a diesel engine there is no current draw after the engine is started, but I'm curious about the technical details of why it happens.

If that is a hard almost Crystal hard, it is a oxide of lead. Clean the terminals real good and cover them with a heavy coat of grease. There may be some galvanic action going on if the cable ends are not compatible with the lead.

My dad has a D-17 allis chalmbers tractor that is 12 pos. That thing will start when nothing else will,on a battery that will not light a flashlight. Once it was running rough so i checked the points.The pads were burnt completely off and the spring,or strap, was blue, but it still started and run! Always wondered if pos ground has anything to do with this.