[tubman]

Actually, the Ford ignition system runs on about 4 volts. At startup, the resistor is cool and offers no resistance so the coil gets a full 6 volts. After running a while, the resistor heats up and develops enough resistance to cut the coil voltage down. Although it is called a "ballast resistor", the Ford resistor functions differently than a regular ballast resistor, so the term is kind of a misnomer.