On a 12 volt tractor a 12 volt coil should NOT overheat and fry.
A 12 volt coil may be labeled "12 volts" or "12 volts no Ballast required" or "12 volts not for use with ballast resistor"
A coil labeled "12 volts for use with ballast resistor" or "12 volt ballast required" etc IS IN REALITY A 6 VOLT COIL AND NEEDS THE BALLAST JUST AS IT SAYS OR IT WILL OVERHEAT
A 12 volt coil will have a LV Primary resistance between little + and - terminals in the range of 2.5 to 4 ohms. A 6 volt coil will be more like 1.25 to 2 ohms
Far as I know as long as Deere still used generators they were still POS Ground and the coil should be wired accordingly