Positive/Negative ground question

[dean333]

When I bought my 37, I noticed the ammeter was reading backwards. I found the battery in backwards, negative ground. I turned the battery around for positive ground, everything then worked fine. Now I have a 33 that somewhere down the line was switched to negative ground. I was going to leave it that way but I ordered LED bulbs for positive ground forgetting it is now negative ground. If I switch the battery back to positive ground is there anything else I have to change? It’s all stock except it has an electric fuel pump added.

[Ken/Alabama]

The LED bulbs I’ve bought were not polarity sensitive.

[dean333]

Ken, I ordered the headlamp bulbs you recommended from Amazon. These are the taillight bulbs I tried tonight, they asked if I wanted + or - ground bulbs. I forgot the car was negative ground when I placed my order

[35Phaeton]

I believe you will have to switch the terminals on the coil.

[35Phaeton]

Only polarity specific items are effected by switching between positive and negative ground. Non-LED bulbs are polarity specific, as are radios and ammeters. Your '37 radio won't work on a negative ground, and as you observed, the ammeter works backwards (it denotes direction of current flow).

[dean333]

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35Phaeton, this is the 33 I have now. It has the stock helmet distributor with a dome top coil. Only ONE wire goes to the coil so what’s to switch?

[35Phaeton]

Originally Posted by dean333

35Phaeton, this is the 33 I have now. It has the stock helmet distributor with a dome top coil. Only ONE wire goes to the coil so whatÂ’s to switch?

In your case, no switch is required at the coil (no way to switch anyway). The change in polarity takes place upstream of that coil. I like those distributors, especially if you use the later set of points. I just sent mine to 3rd Generation for refurbishment and the later points.


There is an old adage that positive ground systems reduce corrosion of the car and its components. I have no idea if that is fact, or fiction.


While you are making those changes, you might want to replace your battery cables with 2/0 wire cables with copper or brass washers.

[ford38v8]

If I'm thinking clearly tonight, you'll need to pull the wire from the ammeter loop and push it through in the opposite direction.

[Ken/Alabama]

Originally Posted by dean333

Ken, I ordered the headlamp bulbs you recommended from Amazon. These are the taillight bulbs I tried tonight, they asked if I wanted + or - ground bulbs. I forgot the car was negative ground when I placed my order

If you bought this bulb for the taillights it’s non polarity.

[Mart]

Nobody has mentioned repolarising the generator. Also the battery terminals are different sizes (if they are the original tapered type) so new cables may be required.

[dean333]

Ken, I bought them from LBcarco.com. They specified positive or negative ground, I was in positive ground mindset so that’s what I ordered. Forgot it was negative ground so they don’t work. I’m going to switch the car back to positive. Thanks.

[Ken/Alabama]

Originally Posted by dean333

Ken, I bought them from LBcarco.com. They specified positive or negative ground, I was in positive ground mindset so that’s what I ordered. Forgot it was negative ground so they don’t work. I’m going to switch the car back to positive. Thanks.

Ok. I also forgot that you needed the pins straight across and not staggered like the ones I pictured.

[injunwiz]

I know this is an older thread, but maybe can get some help without starting a new one. I have a 39 Ford Deluxe I bought a few months ago. It is very stock and 6v but is wired negative ground. What are the advantages/disadvantages of positive vs negative ground? The gauges aren't working now, but that might be another issue as a new factory style wiring harness has been installed. I have a 6v battery and the ground cable won't tighten correctly due to the post size. Also, the car has a Motorola 501a radio and aftermarket heater installed. Do they have to be wired with a 6v negative system in order to work? Neither of them work now. I'm sending the coil out to Skip for a rebuild and want to resolve these issues. Any suggestions and input apprieciated!

[dean333]

Bear in mind Skip had a knee replacement 10/23 and won’t be back in the shop for six weeks.

[injunwiz]

I called him today, thanks though for the heads-up.

[JayChicago]

Originally Posted by injunwiz

39 Ford Deluxe I bought a few months ago. It is very stock and 6v but is wired negative ground. What are the advantages/disadvantages of positive vs negative ground?

Makes sense to switch polarity if the car is being converted to 12 volt, because 12v electrical items are negative ground.

I can't think of any advantage to switching polarity on a car that is to remain 6 volt. Lots of disadvantages: gauges, radio, etc, will only work as designed, positive ground.

Are you sure the car has been switched to negative ground? Maybe just the battery was hooked up backwards.

[injunwiz]

I'm not sure if the battery was hooked up backwards. The positive post has a battery connector with a wing nut on it and goes to the solenoid. Perhaps they switched it to negative ground because of the radio?

[tubman]

The early 6 volt cars were negative ground as it reduced corrosion problems. If the car is six volts, I would switch it back to positive ground. On the heater, you may have to switch the wires around to get it to work. The radio? We need more information. 6 volt Chevrolets (and other GM products) were negative ground, so if you have a radio from one of them, you have a problem. Other than that, it's probably a Ford radio, as I know of no one who makes and aftermarket 6 volt radio. I believe (I'm no expert on this) that the only polarity sensitive component in the radion is the vibrator. We clearly need more information about the radio.

[injunwiz]

Originally Posted by tubman

The early 6 volt cars were negative ground as it reduced corrosion problems. If the car is six volts, I would switch it back to positive ground. On the heater, you may have to switch the wires around to get it to work. The radio? We need more information. 6 volt Chevrolets (and other GM products) were negative ground, so if you have a radio from one of them, you have a problem. Other than that, it's probably a Ford radio, as I know of no one who makes and aftermarket 6 volt radio. I believe (I'm no expert on this) that the only polarity sensitive component in the radion is the vibrator. We clearly need more information about the radio.

The radio is a 1951(?) Motorola 501A universal fit.

[Terry,OH]

Switching battery polarity on the coil is not good.

[injunwiz]

Originally Posted by Terry,OH

Switching battery polarity on the coil is not good.

Skip is going to rebuild the Echlin stock style coil for 6v positive ground application. The coil looks the same as the brown factory Ford script coil.