My apologies to all. I did indeed forget to finalize the Ammeter wiring on the diagram. I threw this diagram together shortly after rewiring my car. The ammeter (on mine) pulls power from the distribution block, and all accessory power comes off the other side of the Ammeter. I opted to connect the coil directly to the distribution block, vs the ammeter. I am sorry for the confusion on that. I will update my diagram and repost it soon.
12v wiring diagram
- Thread starter dbrist
- Start date
My apologies to all. I did indeed forget to finalize the Ammeter wiring on the diagram. I threw this diagram together shortly after rewiring my car. The ammeter (on mine) pulls power from the distribution block, and all accessory power comes off the other side of the Ammeter. I opted to connect the coil directly to the distribution block, vs the ammeter. I am sorry for the confusion on that. I will update my diagram and repost it soon.
Purdy Swoft
Well-known member
I run my 1931 roadster on 12 volt positive ground and no wires needed to be changed . I installed a three OHM coil in place of the original type one point five OHM coil . An original type one point five OHM coil can be used if a ballast resistor is used at the coil connection . The resistor prevents the full 12 volts from entering and burning out the six volt coil in such cases . The larger gauge original size wiring , if in good condition can carry 12 volts better without overheating than smaller gauge wire that is often used on twelve volt applications . Some prefer negative ground for certain accessories . I don't use any accessories and run mine as original . The difference in my 12 volt model A is in the battery and coil . I use the large original cable and wire from the distributor to the ignition switch . I don't use the original pop out switch . I use a more modern ignition switch . I adjust the generator for a 10 amp maximum charge rate . I use the Fun Projects can style voltage regulator in place of the cut out. The Fun projects voltage regulator looks just like the original cut out but gives voltage regulation similar to modern vehicles . Every thing still looks and operates like original but is a more powerfull . I install 12 volt bulbs and use resistors on any 6 volt accessories that are used . I've run the unmodified original starter and generator on 12 volts for many years with no problems . Twelve volt batteries and parts are readily available . I get a more powerful system that still looks completely original .
I updated my wiring diagram and fixed the ammeter wiring. I realize there are many ways to "skin a cat" when it comes to rewiring for a 12v neg ground system. I am simply sharing this, as it works for me and should help others find their way when rewiring. As always, you do not have to follow this exact diagram. It simply gives you an idea of what works. You can add, remove, or change anything to your liking. Thank you all for correcting me and bringing my goof ups to my attention.
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Purdy Swoft
Well-known member
As said , there are many ways to do this operation . I wasn't correcting or trying to say that your method was wrong . I was only sharing and explaining how I did mine .
Yes, but a few wires do need to be changed if switching from positive ground to negative ground. Coil and ammeter wires are two.
Purdy Swoft
Well-known member
I run mine,12 volt positive ground and NO wires were changed , it has worked perfectly for years . If converting to negative ground wires will need to be changed .
Purdy Swoft
Well-known member
In order to run negative ground the battery cables need to be connected as negative - to ground and +positive should connect to the starter switch . This will convert the system to negative ground ..The wires at the coil connection need to be switched and the wires at the ammeter need to be switched . If converting to 12 volt it will be necessary to use a resister at the coil connection or better still use a three OHM coil and no resister will be needed . I use the Pertronix flamethrower coil with great noticeable results . The Pertronix coil looks the same as most replacement coils but gives instant starts and gives extra power that can be felt in the seat of the pants .