Farmall C conversion to 12 volt

I have a C Farmall I am going to convert to 12 volt. I have read and know I need a Delco !0Si altenator one wire I am planning to change the
coil out to 12 volt but do I need a resister back to distributor and points. I have read a couple of different things about that or is there a coil with
a built in resistor. Any comments or suggestions appreciated.

You can get a coil with internal resistor
and it definitely needs a resistor to make the points last longer.

If you use a 12v coil you don't need an external resistor. If you keep the 6 volt coil then you need the external resistor.

Not a flame, just reality. The fact is the coils that need an external resistor say so on the box or can of the coil. This implies that there are resistors in coils that are "12v no resistor required". There are no resistors in those coils they are just voltage correct windings inside. (like putting a 12v light bulb in a 12v car).
6v coils, and 12v coils that need a resistor have about 2 to 2.5 ohms. They are basically the same with different labels. The no external resistor coils are about 4 ohms. When installed correctly, each draws about 3 to 4 amps.
The 6v coil can be used with the ballast resistor on 12v. Thw 12v external resistor coil can be used on 6v systems with no resistor. The 12v no external resistor required coil cannot be used on a 6 v system. Jim

If it we me I would use a Delco 10SI like the one on a 1980 Chevy pickup. 35 amp 3 wire which is easy to wire up and cost around $50 from O'Riely's with a life time warranty

To your good QUESTION

"I am planning to change the coil out to 12 volt but do I need a resister back to distributor and points."

ASSUMING YOURE TALKING ABOUT A PRIMARY IGNITION CIRCUIT BALLAST (between ignition switch and coil input) NOT any current limiting device (resistor or diode) such as is necessary on three wire Delco alternators 1R Excitation terminal to prevent run on even if ignition is switched off

ANSWER NOOOOOOOOOOO

On a 12 volt tractor if you use a "full true 12 volt" rated coil you DO NOT use any additional series ballast resistance, you need to power a 12 volt rated coil at 12 NOT less certainly NOT 6 volts.

HOWEVER if you were to use a 6 volt coil on a 12 volt tractor, YES you would then need a series voltage dropping (12 to 6) ballast or else the coil would run hot and the points burn prematurely.

While they (a few older cars I'm thinking of) used can looking coils that indeed contained a discrete stand alone ballast resistor tucked away inside them, as a past used tractor dealer and farmer I NEVER SAW A TRACTOR COIL WITH AN INTERNAL BALLAST RESISTOR !!!!!!!!!!!!!!!

NOTE you may well require a diode or a resistor or even an incandescent idiot light on a Delco 10 SI family of three wire alternators which is often wired FROM the coils INPUT (from ignition switch NOT to distributor terminal) TO the alternators small 1R excite terminal to receive initial excitation voltage. Without it she may run even when the ignition is off !!! I have used a resistor or a diode or an idiot light but on some tractors they didn't run on even with none of those

Got it ???

John T