Just to add a bit of understanding. The resistance or ballast does in fact reduce the voltage on the coils input, the actual value being based upon the coil itself, and the amount of time the coil is charging(Points Closed). At low RPM's the dwell time is quite high compared to the dwell time at high RPM. When the coil was designed it had to be able to produce a sufficient spark at high RPM so its impedance is matched to draw enough energy at low dwell time to produce suitable spark. At low RPM/High Dwell time, if no resistance was inserted to stem current flow charging the coil, it would eventually overheat and fail. Usually this is accompanied with a bunch of hot mineral oil spewing forth all over your pretty engine. One of the biggest advantages to electronic ignition is called adaptive dwell. The circuitry always maintains the correct dwell time for the coil at various RPMs thereby always insuring a full spark output. Another bonus, no ballast, chokes, resistance wires, etc which can and do change values over time.