model A 12 volt wiring diagram

The "wiring" is no different: Wiring designed to carry 6 V current will safely handle 12 V. However, you do have to change the coil or add a special resistor, all of the light bulbs, either change the horn or add a load resistor, and--depending whom you believe--change the field windings in the starter. ALSO, assuming that you are also switching from positive to negative ground, you will need to reverse the primary wires to the coil.

I'm assuming you're doing this by using a voltage regulated alternator.
 
Just to add to Steves excellent info, If you replace the coil, you will want a 3.0 OHM for 12 volt. I use an epoxy filled coil. If you use an oil filled coil it will need to be mounted with the wire connections at the top. Original model A coils were tar filled . If an oil filled coil is used, oil can leak out and the coil will overheat and fail. If you want to run 12 volt positive ground with an original unmodified generator, NO wires will need to be changed or reversed. If an alternator is used with negative ground, the wires will need to be reversed at the ammeter and coil as Steve said above. I have run unmodified six volt starters on 12 volt since the sixties with no problem. I run a Fun Projects 12 volt can style voltage regulator in place of the cutout on the unmodified generator on my roadster.
 
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Charlie Stephens said:
By all means change to negative ground when you go to 12 volts so you can run all of the modern electronics.

Charlie Stephens
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Some , myself included prefer to keep the model A as original as possible while enjoying the advantages of a superior twelve volt upgrade. If I want electrical gadgets, I'll go in the modern vehicle!!!
 
Come on Purdy, I have a usb charger port for my wife's gadgets. Now she doesn't fuss so much when she goes with me on our trips. :rolleyes:
 
The photo is a simplified Model A electrical drawing. It could be either 6-volts or 12-volts. A 12-volt system is usually a negative ground. In that case reverse the positive and negative symbols at the battery.

A suggested modification to either a 6-volt or a 12-volt system is to disconnect the wire on the right hand brake light switch terminal, fold it back and tape it off. Run a separate wire from the same terminal direct to the load side of the fuse on the starter.

There is no reason for the brake light to receive battery voltage from the light bale. A short circuit in the rats nest of wires in the bale is a likely occurrence. If you are out on a tour you can disconnect the power wire going to the light bale, fold it back and tape it off. You can continue traveling during day light hours and still have brake lights.

Trouble shoot the fault in the light bale later on when convenient.

Tom Endy
 

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CarlG said:
Come on Purdy, I have a usb charger port for my wife's gadgets. Now she doesn't fuss so much when she goes with me on our trips. :rolleyes:
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You are right Carl, I didn't mean to sound pushy. Gadgets are good when you need them, so are alternators to power them. I just couldn't resist pointing out that the unmodified model A generator works good with twelve volts, if you don't need a lot of amps. The generator can easily be repolarized to operate on negative ground. Fun Projects has a negative ground can style 12 voltage regulator. They even have an eight volt regulator. The can styly regulators are as simple as installing the cut out that they replace. I'm still tickled about mine !!! Smiley face !!!
 
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