Ballast Resistor Why?

Because the way Mopars are wired is different from GM/Ford! When the ignition switch is turned to "start" the circuit bypasses the resistor, sending 12 volts to the coil for a hotter spark to get the engine started. In the "run" position, only 6 volts is sent to the coil. As "demon seed" said, many aftermarket ignitions like MSD get rid of the resistor totally.