Correct internal or external coil for pertronix points eliminater

What you say it partially true, but is not the whole story. If it was only the primary voltage and the turns ratio, you would only get a secondary voltage of about 12000 volts (12 volts times a 100:1 turns ratio). The primary voltage of interest is created by the collapsing magnetic field, not the 12V supply. Google flyback transformer operation.

The primary voltage on a points system is basically a function of the speed of changing the current in the transformer (assuming the same coil). See the formula I posted above.

An electronic system is basically the same, except the voltage is also limited by a snubber out the output transistor. For example if the primary voltage is limited to 500 volts, the 500 volts times 100:1 turns ratio is 50,00 volts.

About 100:1 is standard turns ratio for a car coil, I think some of the high performance models may have about 115:1.