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Positive or negative ground

Hi. Im restoring a 1953 Ford F250, 239 Flathead. Installing a new wiring harness. When i got this truck, i got it running snd everything works fine. All electrical, wipers, lights, etc work as they should. (It’s 6V) My question is, the battery was installed with the - negative cable to ground, positive to starter solenoid like modern vehicles are. BUT, the wiring diagram shows it with a POSITIVE GROUND. Do i change it back to positive ground? Will that screw anything up?? Thanks.

If the vehicule starts and work as it should your set-up is fine.Leave it like it is.

Keep it negative ground. I would suspect radio and gauges are setup for negative ground since the truck was negative ground when you started.


I am surprised everything works. Your vehicle was originally 6 volt positive ground.
I bought a 1948 Dodge back in 1977. The battery had been installed with the negative terminal attached to the chassis. The ammeter gauge read backward, but everything else worked, although I didn’t try the radio.
To correct the problem, I discharged the battery completely and then brought it back up with a trickle charger. I repolarized the generator. This is a simple operation. I think I momentarily shorted the battery terminal on the voltage regulator to the field coil, but I am not certain about this. There were two different methods to repolarize the generator depending on whether the field coil in the generator was externally grounded or internally grounded. I have repolarized both types of generators, but I don’t remember which is which. You might be able to find a the book in a library titled “Fix Your Ford” by Bill Toboldt.
If your truck now has an alternator or has a transistor radio, don’t change it. My 1948 Dodge had a generator and vacuum tube radio.

I feel different. I would change it to factory original. The radio, lights, wipers will work regardless of polarity. However, if you have sensors they may or may not work correctly.

@kurtwm1. I don’t think a 1953 Ford truck had sensors. It probably has vacuum wipers. I would even bet that the oil pressure gauge may be mechanical. The temperature gauge may be electrical. It seems to me that on Ford products of that vintage, the temperature gauge went to hot when the ignition key was turned off.
There were no oxygen sensors as there was no catalytic converter. There was no PC valve. There was a road draft tube to ventilate the crankcase.
I am glad the flathead engine is still in the OP’s truck. Like the South, the flathead will rise again!


Sensors on a 1953 Flathead ?


The question I have is:
Are you restoring to factory original or as a fun weekend driver with occasional display at local car shows?
If the latter, you might even consider going to 12 volt negative ground, that does require replacement of bulbs, radio, gauges, etc.
If the former, then back to positive ground for the purists.

If the radio works, leave it alone. The tubes in these old radios require a certain polarity and it can’t be changed, unless you want to rewire the whole radio. If you don’t have a radio in it, then you can leave it or put it back.

I once had a 1960 Borgward with a 6 volt positive ground. No radio. I changed it to negative ground just so I could jump start it from friends cars. To compensate for the difference in voltage, we would touch bumpers and use only one battery cable.

yes, despite popular believes there are sensors, i.e. overheat temperature sensor.

My dad always told me if it ain’t broke don’t fix it​:grin::+1:

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If the starter is now set up to spin the engine in the correct direction (clockwise) as is, reversing the polarity will cause the starter to spin the engine backwards ( unless the overrunning clutch prevents it from transmitting torque in the “wrong” direction. I can’t wrap my head around the physics tonight).


On my 1948 Dodge, the starter spun the correct direction no matter which way the battery was connected.

It seems to me I remember electric motors running in the opposite direction if you reversed the polarity.

I actually have a starter from '48 Dodge on the garage ( along with lots of other parts, I’ll play with it tomorrow).

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In theory you are correct. I’ll test that out tomorrow.

That is correct, the starter motor is a DC motor and will spin the opposite direction if OP connected the positive battery to ground. HOWEVER, if OP also reversed polarity (flipped + & - wires around) on the starter than all would be fine and the starter would spin in hte proper direction.

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I’ve got the starter on the bench. I’ll give it a try. The guages worked, but the charge indicator didn’t.

The heater did, though, and it looks like the wiring was never altered. So i dont know.

No radio, so thats not a problem.

of course not, the needle wants to go in the opposite direction. Flip the connecting wires around and I bet it works. Better start noting changes on your diagram, you might need that in the future.

How do you reverse polarity on an electric motor that only has one wire to it ?