I don't think you need the ballast resistor with the electronic ignition system, even though you are using the 6v coil. The 6 and 12 volt coils have about the same primary resistance. Usually 12-volt electronic ignition systems don't use a ballast resistor in the coil circuit, but some use one in the control circuit. It depends on who made the system you have. You will likely get a weak spark if you leave the ballast resistor in the coil circuit with the electronic setup. Go by the manufacturer's instructions for the hook-up.
The reason for the ballast resistor in the 12-volt contact systems is to protect the points. I'm with Tiny- why not leave the truck 6-volts?
Harvester
