12v + and - ground confusion

H

Hoffman

Junior Member
Background. Purchased an already. Converted 6-12v 31 s/w town sedan three years ago Ran fine until major non-electrical mechanical failure July, 2025. New Schwalm motor and then ran fine again until this July from a loose + post connection and severely degraded 12v battery.

Have now discovered that battery is + ground attached to frame member under front seat front. - cable connected to starter. Now here is the mystery and confusion. When recharging the old battery I connected the positive cable/post hookup to the red on charger, and black charger wire alligator to the frame under the gas tank. Battery charged and car started easily. …..shouldn’t this charging and operating battery hook up be a disaster???

Hoffman
 
Sounds like you hooked it up correctly. Black to negative and red to positive. Most chargers will not charge if hooked up backwards and if you did manage to have current flowing in reverse through the battery you would be in trouble.

Generally the car does not care if it has a negative or positive ground. The ammeter has to be hooked up to show charge or discharge correctly. The generator has to be polarized correctly and any electronics have to be correct, like an electronic cutout or some LED lights. The coil has to be hooked up correctly to provide the spark electron flow from the center electrode to the ground electrode.
 
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Failed to include the installed alternator in the background. In any case it appears that I should just to continue installing the new battery the same way as the replaced one. Appreciate the quick reply. BTW, didn’t know the car didn’t care how the hookup is configured so long as one post is attached to the frame, the other to the starter. Totally unexpected.
Again, thank you, Hoffman
 
Most people run a parallel ground to somewhere on the engine, like a bolt on the transmission. If you are having problems with a slow starter motor you may want to do that.
 
Negative ground is necessary if you will be running any digital electronic devices in your Model "A". Most alternators are setup for a negative ground. You should excellent ground electrical continuity. When checking grounds with a multimeter, measure from the device to the battery's ground terminal.
 

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  • Battery Ground Extra Cable 238kb.jpg
    Battery Ground Extra Cable 238kb.jpg
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Extra ground battery cable work ! even on modern cars . My diesel vw was going through batteries every year and at times difficult to get started , I added an extra battery ground cable to the engine add haven’t had any issues since knocking on wood !
 
The alternator conversion is the key to polarity. The 6-volt GM 11si alternator conversions have a jumper in them to make it work for positive ground. Generally, 12-volt alternators don't have the jumper but some do for those that want positive ground. My 1956 Ford 850 tractor has a standard 11si alternator conversion so I run it negative ground and have the coil connected for that polarity by negative terminal to distributor breaker but I also have the ballast resistor to control the amperage/voltage for a 1.5 Ohm primary type coil.
 
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