Can’t determine battery ground

[Ezombie]

I recently acquired in 1929 tudor that has been stored for 40 years. It was a running car when stored but someone has removed the battery so I have no way to know whether it is a standard positive ground or a negative ground system. Is there an easy way to determine this with no battery present?

[Charlie Stephens]

Install the battery using your best guess. Note the positive post is slightly larger so that might be a clue. Turn on the lights. If the ammeter goes positive you have it backwards.

Charlie Stephens

[nkaminar]

The connectors for the battery terminals are different sizes. I forget which one is slightly larger. Try to fit the connectors and if they do not fit reverse them and try again.

[Bob Bidonde]

It does not matter which ground polarity you decide to run with. After the many years in storage, the generator lost its residual charge. However to be authentic, hook the battery positive terminal to the frame cross-member. After a few minutes of running, the generator will remember the ground polarity you selected.

[Rob Doe]

Are you installing a 12v or 6v battery. If 6v, install as positive ground to the x member. If the car was set up as 12v, negative, the ammeter wires will have been reversed????

[nkaminar]

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Rob Doe brings up a good point. Do you know if it was 12 volts or 6 volts? One way to check would be to take a bulb out of the tail light and hook it up to a 6 volt battery. If it is dim then the chances are that the car had a 12 volt battery. If you hook up the bulb to a 12 volt battery and it burns very bright or burns out then it was a 6 volt battery.

[stevests]

Aren't most light bulbs marked for voltage or check the number if still visible ?

[Jim/GA]

Any car that has been stored for 40 years will still be 6 volts.

The post size is a good clue. I suspect positive ground. Most people were happy to leave the cars positive ground 40 years ago, there was no incentive to reverse it.

Hooking it up backwards from how it is intended to be will reverse the polarity on the coil, which will give a weak spark. The engine will start, but you will want to confirm the polarity of the coil. The starter, the bulbs, even the generator will not care about the ground.

I recently worked on a car with the coil polarity reversed. The plugs were fouled. The owner was complaining of lack of power (which it should not have been -- the engine was a fresh rebuild with HC head).

[ModelA29]

Originally Posted by Jim/GA

Any car that has been stored for 40 years will still be 6 volts.

Any car stored 40 years ago with a generator is probably still 6 volts.
Any car stored 40 years ago with an alternator is probably 12V.

[nkaminar]

Any car stored 40 years ago will need more than a battery. The air in the tires is very old and needs to be replaced.

[Bruce of MN]

That ‘80’s air was pretty good, so I’m not sure about that.

[Jim/GA]

It would be nice if the Original Poster came back with what they found, photos, etc. Otherwise we are all just wasting our time.

[rotorwrench]

Look for a ballast resistor connected to the coil. 12-volt conversion would require that on an original type 1.5 Ohm primary type coil. If the coil is modern then it could be a 3-Ohm type for 12-volts.

40 years dates back to 1984, A lot of stuff was available back then. The generator could tell a bit if it still has one. The converted GM 10si alternators were available in 1984.