12 volt aux battery grounded to frame??

W

wcmill

Member
Hi guys, this is my first post and am happy to be aboard……WHAT A FANTASTIC SITE!!
I finally bought my first Model A about a week ago. Have been a dedicated muscle car guy (still am) but love the A…..so simple.
So first of I’m sure many questions:
For clarity my car is a 31 deluxe roadster. It was fully restored about 9 years ago, driven for a few years then stored. I’m in the process of changing fluids, timing, gas tank rust removal, etc. the previous owner installed a small hobby battery to run the 12 volt signal lights that were installed. For whatever reason he grounded the neg terminal to the firewall, and installed an inline switch on that line.
The car itself is the original 6 volt positive ground..
Would this not create havoc or issues with the ignition or for that matter anything else that’s operated by the car on 6 volts?
So you have a big 6 volt car battery grounded positive…..then a smaller 12 volt grounded negative…but to the same place (the frame). Would they not be in conflict with each other in some way??
I haven’t started the car yet….however the signal lights do work fine.
 
as long as the 6V and the 12V wires never connect to each other neither know about the other
My MG had + ground, the radio had - ground through a converter, the car and the radio shared the same ground, everything was fine until a speaker grounded itself, then the smoke came out of the speaker.
 
It may not affect the cars normal system just by using the same ground plane. The polarity won't be an issue since the power side of the circuit is not shared with the normal system. A good indication of problems would be to watch the amp meter when this 12-volt system is in operation. It probably should have been isolated but it may have no affect unless the another electrical device is inergized too close the the system while in operation.

A lot of reproduction lighting for the model A cars is going toward LED lights now days and they aren't as voltage sensitive as incandescent lights. Some of this stuff may not have been as available 9 years ago. A person might think about converting it to LED with 6-volt positive ground circuitry. This takes a lot of load off the original system since LEDs use only a fraction of the amperage of the old incandescent bulbs. The wiring can remain the same but bulbs and possibly the signal stat would be the big change. Some signal stats are electronic and some are bi-metallic thermal breaker activated. The ones with the thermal breaker sometimes need resistors to make them work correctly. The electronic or electro-mechanical types will usually work with low current draw systems.
 
Thanks for the quick reply fellas! I guess I’ll wait and see what happens once I get the car running.
I like the LED idea.
 
Welcome, I too come from muscle cars, still have a couple. I love driving my 30 Roadster Deluxe which sounds very similar to yours, restored then put away. I went through timing, spark plug gapping, re-torquing everything, etc. This is a great site and YouTube have been very helpful in learning about the Model A world.
 
Depending on what type of signal lights and controls are on the car it might be wise to convert the signal lights to 6 volt positive ground.
 
katy said:
Depending on what type of signal lights and controls are on the car it might be wise to convert the signal lights to 6 volt positive ground.
Click to expand...
Correct....But make up your mind and go all 12v or all 6v.. A combination is just inviting trouble.
 
I am currently restoring my 6V Tudor + ground.

I will be experimenting using a 6V to 12V electronic converter and use the frame for ground on the 12V circuit for power to turn signals and park and brake lights.

I do not anticipate any problems with the setup and the 12V will not be dependent on a separate battery so no need to charge a second battery.

Starter / Headlights / Horn / Alternator / Ignition will remain 6V.

10AMP version on Amazon search for DIGITEN DC 6V 5-11V to 12V
 
airjam said:
I am currently restoring my 6V Tudor + ground.

I will be experimenting using a 6V to 12V electronic converter and use the frame for ground on the 12V circuit for power to turn signals and park and brake lights.

I do not anticipate any problems with the setup and the 12V will not be dependent on a separate battery so no need to charge a second battery.

Starter / Headlights / Horn / Alternator / Ignition will remain 6V.

10AMP version on Amazon search for DIGITEN DC 6V 5-11V to 12V
Click to expand...

.... but why not just use 6 volt turn signal, park and brake lights? They work just as well as 12v. Also, be careful with that inverter.

I think the inverters you are looking at use separate common (ground) circuits. In other words the positive ground input cannot be tied to the negative ground output. If that is the case, you would need to run an isolated negative to the lights and not touch the body of the car.

I have one of those to drive a cigarette lighter socket. I cannot let the negative output touch the metal car body.
 
Bill G said:
.... but why not just use 6 volt turn signal, park and brake lights? They work just as well as 12v. Also, be careful with that inverter.

I think the inverters you are looking at use separate common (ground) circuits. In other words the positive ground input cannot be tied to the negative ground output. If that is the case, you would need to run an isolated negative to the lights and not touch the body of the car.

I have one of those to drive a cigarette lighter socket. I cannot let the negative output touch the metal car body.
Click to expand...

Thanks for that information. I was concerned about common ground. I will have to check into that. Want the convenience of having a 12V circuit to run 12V accessories. I am not a purist and plan on common 12V turn signals which are much cheaper than the 6V aftermarket Model A style.
 
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