So basically the car uses all 12V to start but once its up and going the ballast resistor drops it down to something around 6V? Is this close to the right idea?
Yeah,run is about 6.7 volts. If the 12 volts was continuous the coil would over heat. You can run it with the resistor bypassed for a short time though.
I've went 20 minutes drive to the part store with a jumper before.