Farmall cub 12v conversion with j4 mag

Delig · Jul 25, 2023

I have a rebuilt j4 magneto with an internal coil.
I also have a 12v gm alternator kit with a ballast resistor. Can I use the internal/rebuilt coil or do I need to bypass it with a 12v ignition coil with the resistor?

Tramway Guy · Jul 25, 2023

The coil in a magneto is not connected to the battery in any way. So no need to do anything.

Delig · Jul 25, 2023

Sweet. TY.

Steve@Advance · Jul 25, 2023

Your simplest solution would be to get a 'One Wire' alternator.

If the tractor came with a magneto, the only function of the ignition switch is to ground the mag to kill the engine. The alternator you have requires a battery connection through the ignition switch to excite the alternator, and break the connection with the ignition off. It can be done, but it gets complicated and more expensive than getting a 'one wire'. A 'one wire' is the simplest install, as the description says, only one wire to connect directly to battery voltage.

Under no circumstances is the mag to be connected to the electrical system! It will be instantly fried!

used red MN · Jul 25, 2023

Hello Delig welcome to YT! If you want to use a 3 wire alternator that requires a powered excite circuit. There is a way to use a switch operated by oil pressure to provide a circuit for this. If this is something you want more details on post back with a request.

tractorguy2 · Jul 25, 2023

That is how my dad use to put alternators e Farm all M and H tractors with a mag.

Farmall cub 12v conversion with j4 mag

Delig

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Tramway Guy

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Delig

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Steve@Advance

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used red MN

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tractorguy2

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