6 volt NEGATIVE ground? 1955 tbird

[ion]

I was doing some electrical work on my recently acquired ‘55 tbird and discovered that in this car the negative end of the battery is connected to ground. These vehicles are supposed to have positive ground. It’s not a 12 volt conversion, it’s still a 6 volt battery. Why would someone have done this? You can’t just install the battery backwards can you? All the gauges work properly and the car runs well. Anyone see this before?

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[uncledar]

I bought a 55 thunderbird and had the same problem, changed it back to positive ground. The clock and radio won't work. You're right everything else worked fine.

 

[Gary Tayman]

Every 6 volt Ford that I know of used positive ground. However these expert mechanics of today don't even know what 6 volts IS, let alone positive ground. Gee, the negative terminal always goes to the frame, right? The funny thing is, the lights still work, the gauges usually still work, the starter works, and even the radio (with original mechanical vibrator) will still work. But I'm usually the one who hears about it because I work with the radios. A repair usually includes replacing that vibrator (which only had an expected life of 18 months!) with a modern one, and stereo conversions use a power booster which is wired for positive ground. For whatever reason, I get the calls from Studebaker owners -- "My radio was playing great, but I just had the car service and now it won't play at all!" BATTERY BACKWARDS! Best to put it back where it belongs.

 

[CSPIDY]

The biggest problem is the ignition coil polarity will be wrong and you won’t get a very hot spark.

 

[ion]

Thanks folks, sounds like the advice is to put it back the way it ought to be, and I can see how some less knowledgeable person could easily put the battery in backwards when replacing it. But I’m surprised there’s no major consequence of the polarity being reversed. Pardon my potential ignorance, but wouldn’t the starter crank the engine in the wrong direction, for example?

 

[cokefirst]

Changing the ground from positive to negative will affect the radio, clock and the blower motor of the car. The gauges will work because the flow of current will not affect their operation since they work in the D'Arsonval principal that uses a variable current to operate the gauge by changing the the resistance of the sensor. The clock is probably not damage but the radio may be. Convert the vehicle back to positive ground if you plan on repairing the radio. The generator will work either way, and just needs to be polarized to change it from negative to positive ground.

 

[Gary Tayman]

On the radio, to clarify: The original tube radios for these cars will work with either positice or negative round. In fact, the 1947-53 Chevy and GMC trucks used the same radio (the only exception is the dial markings) and the Chevy is negative ground but the GMC is positive. The 6 volt power goes to the tube filaments, essentially the same as light bulbs, and will work either way. It also goes to the vibrator which converts it to 6 volts AC -- to a transformer, and rectified, filtered, and outputs about 230 volts D for the tube plates. If the vibrator gets replaced, the new ones are solid state and they DO require correct polarity. If it is the AAR design, reverse polarity can damage it. If Aurora, it won't get damaged but it won't work either.

 

[ion]

Thanks everyone for the replies. Apart from the tip about repolarizing the generator it looks like the flip back should be a simple one. No radio in this car so no problem there. In fact I discovered the problem while trying to install one. What about the starter motor?

 

[ion]

Answering my own question:

“Most starters are a universal motor, meaning the magnets inside are actually electromagnets that are energized by the current from the battery. Reversing the input polarity will reverse the electromagnets as well as the armature, resulting in the motor spinning the same direction with either polarity applied.”

 

[Critterpainer]

As you have found out there is no problem reversing the polarity on an original car. Yes having the polarity of the coil corrected will help the coil throw a hotter spark, but most won't even notice. I also own a Nash Metropolitan which is a 12V Positive ground car. I spent minutes on the arduous task of turning the battery around, switching the wires to the coil and polarizing the generator. The only thing that can trip a person up is if you have an aftermarket amp gauge. It will read backwards. The reason I changed the polarity on the Metro was the danger of another person jump starting it or plugging an electronic device into the cigarette lighter.

 

[ron56]

Trivia: Which other American vehicles used 12 volts positive ground besides the Nash Metro?

(Jeopardy music playing)

The 1955 Packard, and some 1955 GMC trucks.

I had a 1953 Studebaker that was 6 volts with a positive ground.

 

[Critterpainer]

My "American" Metropolitan was built in England for the US market.😉

 

[Doobie]

I bought a 55 thunderbird and had the same problem, changed it back to positive ground. The clock and radio won't work. You're right everything else worked fine.

I also have a 55 that has a 12 volt starter and 6 volts for everything else ( two six volt batteries in series). It has an alternator And is Positive ground. Do I have to change polarity of alternator if I switch to traditional 12 volt?

 

[4VE]

How did you set up the circuit? 2 batteries? How do you charge them both?

 

[Doobie]

How did you set up the circuit? 2 batteries? How do you charge them both?

 

[sylvurhfox]

I also have 2, 6 volt batteries wired in with a series parallel switch. I used the switch that is sold with the battery that has 2 batteries in one.
I mounted the second battery behind the seat and ran 2 0 cables.

 

[4VE]

Are you charging them from the generator using two 6V leads from voltage regulator? I see 5 yellow on the N in series that would be 12V and 1 white on the other N and what appears to be a black lead that may be joined to the white? This permits both 12 and 6 V?

 

[paul5456]

Having two batteries (plus having the second one behind the seat) seems the worst way to go. Easier to just go with 12 volt all the way

 

[Ward 57]

I also have 2, 6 volt batteries wired in with a series parallel switch. I used the switch that is sold with the battery that has 2 batteries in one.
I mounted the second battery behind the seat and ran 2 0 cables.

Sounds like a little overkill but if you pulled it off.. Kudus.

 

[sylvurhfox]

I have had this system for close to 25 yes. Still works good.