You will need to put a resistor in the power supply wire to the coil!! Many coils on 12V cars are/were 6V coils. The wire from the starter solenoid to the coil supplies 12V for cranking/starting purposes and when the starter disengages the coil circuit will drop back to 6V to run. Many 12V vehicles that get modified and 6V vehicles the get upgraded to 12V have problems starting because builders neglect to run the starter boost wire when they build their ride. Others burn up ignition coils because they have run 12V to a stock style coil that's designed for 6V operation.

Never use a minor caliber bullet on a major caliber adversary