I have had good luck with the three pertronix ignitions that I have installed. Whether or not you need a ballast resistor depends on your system voltage, the number of cylinders, and the total resistance of your coil and ballast resistor. I recommend limiting the DC current to ~4 amps for a 6 cylinder. This means a 3 ohm coil if you do not have a ballast resistor (12V). If you are using an original 1.5 ohm coil, add a 1.5 ohm ballast resistor.
Edit: These recommendations are for the original Pertronix, not the Pertronix II.
