The Stovebolt Site Forums The Shop Area The Electrical Bay neg vs poss?

Why are Chevy's and GMC's of the same year grounded differently?

Because that's the way they made them. If you don't like pos. ground connect it up the other way. Make it neg. ground.
I'm betting someone comes in with the technical aspects of why it was done either way.
I changed two of my tractors from pos to neg and they don't know the difference.

Dan

I think the answer "that is the way they made em" is about as good as it gets from a technical aspect. Light bulbs and motors will not care if you change from neg to pos ground. What may care is a generator that is used to one way and if I recall correctly while your ignition will work it is hard on teh contacts when you change grounding.

Best bet LEAVE IT ALONE
MARK YOUR BATTERY POSTS WITH PAINT
MARK YOUR POS POST CABLE WITH RED TAPE

Dan Bentler

Excellent advice, Dan

At one time, it was believed that commercial vehicles would have fewer grounding and corrosion problems with a positive ground system. That's not very likely, but it represents the engineering theories of 60+ years ago. If you decide to switch the ground polarity, swap the wires on the coil primary so the + lead is connected to the ignition switch, and the - terminal goes to the points. Also, re-polarize the generator by momentarily touching a jumper wire from the Battery terminal to the Armature terminal at the regulator. The regulator is supposedly polarity-sensitive, but I've seen a lot of them work OK on reversed polarity. It's possible to buy aftermarket regulators that are designed to work either way, but try the original one first. If it was my vehicle, I'd leave it original, and just mark everything so it's obvious what the ground polarity is.
Jerry

Hope I can get a question in here.
I am not sure about other year Chevy trucks but on my 3100 235 engine...why is the coil face down in the manuals? Was there a reason? With mine, my dad put it face up .

GMC as well as most larger trucks used a positive ground because lights, especially on the trailer, loose ground a lot quicker due to corrosion of dissimilar metals with negative ground. In fact Freightliner used positive ground until the 70's when drivers got electronic gadgets such as cb radios and demanded negative ground. Most trailers today are built with 2 wires going to each light instead of grounding to the chassis. GMC was built as a big truck while chev didn't get bigger than 2 ton until the task force series. Trucks did have less grounding problems with positive ground. I was driving them and fixing them in those days. I don't want to go into a lengthy discussion, but if you read about corrosion between two unlike metals, it all depends on which way the current if flowing.

I think the upside-down coil was an effort to prevent condensation from collecting in the high-voltage tower of the coil, back when plug wire boots left a lot to be desired in the waterproofing department. Of course, the distributor cap had six plug wire terminals, plus a coil terminal to collect moisture, all facing up, so the theory was flawed, IMHO!
Jerry

Jerry,
Good to know. I was curious about that. But makes sense to me. I am hanging mine upside down like the manual! Crazy stock original look guy here!