As JohnZ suggested, the Pertronix unit "wants" a 12 volt source; wiper motor is one possibility, straight off of the battery is another.
However, if everything else is in good shape, using the reduced "ballast" voltage shouldn't keep your car from running or starting. If your car won't start and run, you probably have something else other than low primary voltage, unless your primary voltage is consistently dropping below 8 volts.
On both my 66 Chevelle as well as my 69 RS, I have made the conversion to the Pertronix Ignitor electronic ignition with their flame thrower coil and all works just fine with the resistance (ballast) wire in place. According to Petronix, their electronics package is designed to operate between 8 and 16 volts. In the stock setup, when the engine is running you do not have a full 12 volts at the coil +terminal due to the resistance wire being in the circuit. Hence, JohnZ's recommendation to connect directly to a 12 volt source, which is a very good suggestion in that it ensures that you will always have enough primary voltage. However, I have checked both of my cars and I have between 9 to 9.4 volts and both cars run just fine. However, neither of my cars are performance rides, so neither car ever gets pushed very hard.