To operate an ignition coil on a 12 volt tractor you need a full true 12 volt rated coil. Such will have a LV Primary resistance of around 2.5 to 4 ohms (many 3) as measured between its little + and - terminals.
If your coil measures say 1.25 to 2 ohms from + to - its like a 6 volt coil and will overheat badly on a 12 volt tractor plus the points will burn prematurely.
If your coil measures like a 6 volt coil above you can add an external series voltage dropping (12 down to 6) ballast resistor and that will stop the overheating. Typical old farm tractor ballast resistors (for using a 6 volt coil on a 12 volt tractor) are around 1.25 to 2 ohms.
Contrary to some beliefs, typical old farm tractor coils DO NOT have an internal discrete stand alone ballast resistor tucked away hidden inside the can. THERES NO INTERNAL RESISTOR !!!!!!!!!!!!
NOTE a full 12 volt rated coil may be labeled "12 Volts" or "12 Volts NOT for use with ballast resistor" HOWEVER if its labeled "12 Volts for use with ballast" its in reality like a 6 volt coil and needs the ballast just like it says or else it will overheat.
YOU NEED TO INSURE YOU HAVE A FULL TRUE 12 VOLT COIL !!!!!!!!!! Measure its LV Primary resistance from + to - to see if its 2.5 to 4 ohms !!!!!!!!!!!!!! If its a 6 volt coil (1.25 to 2 ohms) add a series ballast
Coils can also overheat if the voltage is too high like 15 to 16 volts CHECK YOUR BATTERY VOLTAGE WHEN RUNNING..
Coils can overheat if not heat sink mounted properly or in an extreme hot environment where they shouldn't be mounted..
Since this is a Tractor NOT an old car forum and you mentioned tractor, I PURPOSELY spoke of typical old farm TRACTOR coils Not automotive coils.
If I missed anything hopefully the other fine gents can add to this
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Today's Featured Article - Good As New - by Bill Goodwin. In the summer of 1995, my father, Russ Goodwin, and I acquired the 1945 Farmall B that my grandfather used as an overseer on a farm in Waynesboro, Georgia. After my grandfather’s death in 1955, J.P. Rollins, son of the landowner, used the tractor. In the winter 1985, while in his possession the engine block cracked and was unrepairable. He had told my father
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