The Stovebolt Site Forums The Shop Area The Electrical Bay Positive ground system

Just out of curiosity. In the older vehicles with a positive ground, are there any components that are polarity dependent? Is there any reason you couldn't just flip the feeds and go negative ground? I will stand back and watch the bar fight.

Definitely! There were some...and as I recall some were designed with diodes to prevent folks from hooking them up incorrectly and frying them. Radio was an important one as I remember. Hook it up wrong and unless it had diode protection it was gone. Clock was another...in some vehicles it didn't like to be hooked up incorrectly and while it wouldn't kill it, it no longer worked okay. Heater motors/fan motors don't necessarily care. Some folks would claim coils were affected but others would say they weren't. My advice is: hook them up correctly and don't reverse the polarity. When you get down to basics, they're a step-up transformer.

Really all you're doing is changing the direction your electrons go but any solid state device or any device using discrete electronic components will NOT like this. An old explanation was "imagine you change things so that you sleep on your commode and then if you need to tinkle you walk over to your bed to do that."

Dave,
I am no electrical expert but I do want to share a couple anecdotal experiences;

With a brain that went blank, I was replacing the battery in my 1947 Model 509 Diamond T and installed it with the negative post grounded. It is a positive ground truck. Upon turning the ignition switch on, and before I could hit the starter button, I heard quite a racket coming from the firewall. I had totally fried the original Autolite voltage regulator.

After driving from Minnesota with my newly acquired 1950 Chevy COE, I was unable to start the truck to get it off my trailer. The engine turned over, I fiddled with various switches, tried the lights (they came on), ect. Would not start. In the middle of the night I woke up and was pondering my dilemma. I recalled that the ammeter went to charge with the lights on. At first light I went out, switched the battery polarity (it had been installed by the previous owner with the positive post grounded). The truck started right up. I have since learned that reversing polarity drops the voltage from the coil but that it may run fine.

I assume that Delco and Autolite regulators are not identical and that the latter are not tolerant to polarity reversal

Agree above Electronics is the biggest one. older generator, some starters (other than direction of spin which could be set) and lights did not care. (other than the age old arguments aka bar fights found all over the web for what corrodes what does not)
the biggest reason the moved to negative ground was electronics and the money that is around that. The big three and this is a generic three had to agree on a standard. (in their respective countries) hence why north America when negative ground.
and England and a few Europeans stayed with positive ground. The standardization allowed for a lot of creature comforts without having to chase manufacture part specific (they did not have to either with sourcing vendors).

I have fried a few radios back in the 80s when a few friends had some older British cars and we forgot to check which ground it had.

Google positive ground vs negative ground and you will not find much of a one size fits.
But if you dig deep enough I bet you find money is the answer.

Ground polarity can be switched, but you'll need to do a couple of things in the process- - - -repolarize the generator by momentarily connecting a jumper wire from the "BAT" terminal on the regulator to the "ARM" terminal, (1/2 second or so- - - -you'll get a big flash, which is normal) and reverse the wires on the coil primary terminals. You might need to swap the wires on the back of the ammeter to make it read "Charge/Discharge" correctly. Voltage regulators will sometimes, but not always give problems when running in reverse polarity. Starter, heater, and electric windshield wiper motors usually don't care which polarity they get. I believe the old vacuum tube AM radios were polarity sensitive- - - -modern solid state ones definitrely are!
Jerry