Correct ballast resistor

When you start using aftermarket coils, then you have completely changed the engineering. There is no guarantee that some other coil will work. Only way I know is "what has worked" for others and "what has not" caused coil/ box failures. There are several possible issues........

1....The ECU may not be able to handle additional coil current
2.....The box may not have low enough resistance to cause the coil to saturate
3.....A given resistor/ coil combination may cause coil or box failure or not allow enough current to generate even as powerful spark as a stock coil

There are some coil combos over the years---the big old rectangular Mallory was one---that used your stock resistor AND the supplied Mallory resistor. So they actually drew LESS current than stock