A ballast resistor limits limits the maximum coil current. The maximum coil current = battery voltage / (ballast resistance + coil resitance + wiring resistance). If the coil resistance is decreased, the current increases. The power dissipation in a resistor, P = I * I * R, where I is the current and R is the ballast resistance. I * I is current squared. An example is if the current increases by 20%, the power dissipation increases by 44%. The solution as other have stated is to use a standard coil, or increase the value or power rating of the ballast. The elevated current may at sometime cause failure of the orange box transistor. The use of a MSD box is also an excellent idea. The MSD box charges a capacitor to a high voltage and dumps it into the coil that works as a transformer to step up the voltage for the spark. No ballast is required.
More modern ignitions propery control the dwell and limit the current by limiting the charge time. A ballast is not required. The dwell is a predictive thing done with micro controllers. Proper dwell control achieves correct charge current at the correct time for the spark. The older means in the orange box uses older and dumb analog means and results in undesirable excess dwell. The ballast is a band-aid to limit when the coil is prematurely saturated.
As a hobby I build high performance ignitions that do not need distributor caps and rotors. They are able to be easily tuned with engine running. They have three dimensional spark advance tuning. The available spark energy is not limited at high rpms since multiple coils are used. The multiple coils enable dwell overlap, not possible with single coil ignition.
