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To Ground + or not?


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For all practical purposes they are the same. I have only ever heard one sensible reason for preferring one over the other. The positive post always gets more corroded than the negative. For some reason this was much more pronounced on the old cars. Well if the positive cable is going to corrode and rot off, it is a lot easier and cheaper to replace a 1 foot long ground strap.

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The majority of US cars and trucks built prior to the 12-volt change-over (1955-'56, except for Buick, Caddy and Imperial in '53), were six-volt, POSITIVE ground...

From what I recall from previous research in old MoToR's manuals, the major exceptions were:

Buick, Chevrolet, Oldsmobile, Pontiac, Reo, and Willys.

Caddy and GMC were positive ground, as were all MoPar, Hudson & Terraplane, Ford -Lincoln-Merc, Packard, Pierce, Graham, Hupp, Nash, Kaiser-Frazer, Studebaker.

I've seen/heard a theory that positive-ground systems tend to experience greater corrosion at connections to chassis grounds: ie at lights, and other accessories.

I have not personally had that observation - I have found that corrosion at chassis grounds is more a product of exposure to weather / road crud.

Regardless of which terminal gets grounded, it seems that the positive post of the lead-acid battery always develops a very hard black coating, whereas the negative terminal just becomes a dull gray. I wonder if this happens with Optima batteries ?

Lastly, from the dim memories of my High-School science classes, I seem to recall that the "natural flow" of current is from the negative terminal to the positive terminal in a battery/galvanic system.

Same goes for vacuum tubes in electronics (the emitter(cathode) has a negative charge, and the collector( anode, "plate") has a positve charge, to attract the electrons.

Or, the tradition might have been established in the early electrical industry (Edison always favored DC current, even for municipal systems), and electric traction systems (streetcars and interurbans) ran on DC current...

I would hazard a guess that this was why early autos were positive ground...

I have never encountered a vehicle with 12-volt positive ground ( although I wouldn't be surprised if they existed in Europe).

Aside from which terminal is "insulated" ("hot") and which terminal is grounded, the two systems function exactly the same way: energy moves from an area of high potential to an area of low potential (similar to analogies using water / air "pressure" or temperature).

Devices that work on resistance (incandescent bulbs, resistors, bi-metal gauges) don't seem to care about polarity; devices involving magnetism, capacitance, and/or diodes (generators, alternators, coils, condensors, regualtors) do care about polarity, and either become damaged or won't work if installed against their design polarity.

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British cars were 12v Positive until I believe 1968. With some exceptions, US cars were 6v Pos until WW2.In 1946, All GM cars went to 6vNEG except GMC. In 1953 Caddy and Olds went to 12vN, but Packard in 1955 was 12v Pos. and went to neg in 1956 with the rest of the US. VW stayed 6v neg until 1967.

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Thank's to all who are replying. The 36 Divco I'm working on has a positive ground according to the wiring diagram I have. It won't have such high level options like a radio so that is not a problem. I was concerned about gauges, etc.


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From an operational standpoint, as long the electrical components and wiring are in good condition, there's no difference between positive and negative ground - they both "work".

Some of the early AC electric gauges ( 1930's) were magnetic, and might indicate "backwards" if the polarity were reversed at the battery...

I've had no problems with the 6-volt positive-ground systems in my pre'56 MoPars...

I believe there are inverters & converters to adapt negative-ground and 12-volt accessories to 6-volt positive-ground systems.

Not sure I understand the advantage of changing polarity to negative ground if you're staying 6-volt...

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British cars were 12v Positive until I believe 1968.

The British chageover began in the mid-1960s, and by 1968 it was complete. Jaguar and MG were the last holdouts.

A lot of guys with British cars switch their polarity to add modern radios, however there are at least 2 other reasons. Electronic ignitions systems for positive ground are rare (Petronix makes some for common applications, but I don't know of any others). Also if you have a car that needs a blower motor and can't find one, a negative ground motor can be substituted without surgery to the wiring harness if you reverse the whole car's polarity. Otherwise it will run backwards.

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