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Help with battery and 6 volt positive grounding


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I have been running my car (1951 Plymouth Cranbrook) for over a year now with the negative terminal grounded to the engine block. That is how the car came when I bought it. The battery is very old and does not hold enough of a charge any more and so I decided to replace it. I bought an Exide 6 volt.

When I bought the battery, I was reminded that the car is a positive ground. So I scratched my head and wondered how is it that its worked all this time.

I am really bad when it comes to electrical stuff. Can anybody help. How do I know if my car is still a positive ground? Could it have been converted at some point to a negative ground? What will happen to this battery if I run it with the negative grounded on the block?

Really confused and in need of help.



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Most of your items don't care if they are run + or - grnd. The radio, needs to be pos grnd, the rest would do okay with - grnd.

If you choose to return to pos grnd, you have to polarize the genny, switch some wires around on the ammeter,coil, and battery, pos grnd to engine, - bat cable to solenoid and starter motor.

If your system is working fine on negative ground, just buy a new battery and continue to operate that way, or return to pos ground, does your radio work?

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Or you might need to do nothing as only the battery may have been installed incorrectly.

Lots of oflks just assumed that all systems were negative ground.

6V systems rely on current flow. The primary batterycables should be nice and thick and not like what is on your 12 V cars. 6V stuff is also sensitive to proper grounds at the load like the lights. So good clean grounds are important to maintaining proper current flow.

The only real problem with a backwards installed battery is premature ignition point wear.

and an incorrectly indicating amp gauge. Double check to see that the (+) terminal on the coil goes to the distributer, and the (-) terminal is conected to the ignition switch side.

Electrical motors used in cars have temporary magnets that get switched on with the ign and are polarity neutral. So the genny, the heater fan, the starter motor don't care which way power flows.

Do a search for generator polorizing the genny, and install the battery correctly.

The amp gauge needle should go toward the Neg sid with the ign on and the headlamps on, and then show a slightly positive indication after starting and with the engine runig above idle. If the gauge reads opposit, a trip under the dash (with the battery disconnected) will be necessary to swap the wires on the gauge terminal posts.

You might need a new set of points if the car was driven alot with the polarity switched.

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When I purchase my car the previous owner had the battery hooked up backwards. The car ran fine but not great and the radio didnt work. I learned that the coil will still work when connected backwards but will only work at a third of its potential capacity. I swapped the leads on the battery, polarized the generator and voila, everything works great. And now the radio works.

This is a diagram for a p-15 but hopefully it will help a little. :D


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the diode plate is everything on the alternator...they are not interchangable between + and - setups..so if yours is working, look at the battery connections and see which terminal is going to the engine block..that alone will be the answer to your question..outside a manufactuer's name and part number to cross reference...

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I have looked. The negative terminal from the battery is going to the engine block.

I was having problems with the charging, but i had work done on the voltage regulator. It stopped being a problem. I then let the car sit for some time while I was out of the country and then out of the state on business. It was having a really hard time starting the car with the cold weather and the like and so it I had to keep recharging it. Once the car was running it ran great all day long. It was after it sat for like a week or two that it was having trouble getting started again. So i would drain the battery trying to start the car. It eventually just crapped out and would not recharge any more.

What I'm understanding is that I can run the battery with the set up as is and not really be doing any damage. I should look at the wiring and follow the connections and see what the situation is. My car does not have a radio so that is not an issue.

Everything else works fine when the battery is charged and running. Will this new battery just lose its charge over time? Will I be back in the same mess in a few months?

Thanks to all the responses. Sorry if I am not getting the electrical stuff, like I said, I suck at that and know my limitations.


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So, will hooking the radio up neg. ground ruin the radio? When I got my car it was hooked up neg. grd. I got it back in proper order and everything works except the radio.

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So I went over and helped look at his Plymouth. We checked the coil, + went to the distributor. We swapped the battery around to + ground. We then flashed the ARM to BAT on the VR. Car started just fine. We couldn't check the current coming out of the VR to the battery as the tester wasn't working.

I have a couple questions. When I polarized the generator in my 53 Desoto, I actually hooked the battery up to the generator and it spun for a bit. I forget the exact process, what connects to what. Does this need to be done to the gen in the Plymouth? When I flashed the VR, it sparked for a sec.

Also what would have caused this. He has a JC Whitney fuel sending unit he converted to work in the gas tank. It worked for a couple weeks, then read as "FULL" permently. When we swapped the battery, it now reads "EMPTY"

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