The Differences Between a 6 Volt and 12 Volt Ignition Coil 

Do you have a 6 Volt or 12 Volt Ignition Coil? Can you run a 12 Volt Coil on a 6 Volt System? How do Contact Breaker Distributors work? Why do you need a resistor on a 6 Volt Ignition Coil?
FORD CL340 Skid Steer Restoration Project "Rust Bucket Rehab" Ignition Coil and Distributor Cap
How to tell a 6 volt coil versus a 12 volt coil. A 6 volt ignition coil system generally operates with a ballast resistor and a contact breaker or point distributor. As the distributor spins the contact points touch and release with the timing of your spark plugs causing an arc of energy to ignite the sparks. The resistor ballast retains energy and releases it in timing with the distributor. This build up of energy takes the 6 volt charge of the ignition coil and ramps it up to a 12 volt discharge to fire your plugs. You can remove the resistor ballast and use a 12 volt coil. Using a 12 volt coil will send a continuous flow of energy to the distributor making the timing easier. However over time it will burn out the contact points on the distributor.