[CWPASADENA]

The original Ford coils were not 6 Volt but somewhere nearer to 4 Volts. When the engine is running, the resistor in the system drops the charging system voltage from apx 7 volts to the design voltage of the coil, apx 4 volts.

The use of a low voltage coil and a resistor is to help insure adequate spark during starting, especially if the engine is cold.

The ignition resistor is a high temperature wire that will heat up when currect is passed thru it. When cold, the resistor will have very low resistance but as it heats up, its resistance value will increase.

When cranking the engine, the battery voltage will drop but beings the resistor is also cold and will have low resistance, the coil will have adequate voltage to provide enough spark for starting.

As soon as the engine starts, the battery voltage will increase to a value closer to that of the the charging voltage, apx 7 volts. As the engine warms up, current thru the resistor will cause it to heat up and as a result, its resistance will also increase thus dropping the voltage to the coil back to its design voltage of apx 4 volts.

GM and may be other manufacturers used a simular system, a coil designed for lower voltage then that of the charging system, and a "Ballast" or dropping resistor. During cranking, the starter solenoid had an additional contact to provided direct "Battery Voltage" to the coil. Thus, there was a hot spark for starting while cranking the engine but the coil (in combination with the resistor) would operate at its design voltage while the engine was running.

In the "Old Days" when a guy was having trouble getting his Ford to start, he would often have someone yell at him to "Put a Nickel In It". This came from the situation when (especially if the car was hard to start) the engine was cranked for a while and the resistor had warmed and increased in value to to the point where the coil was no longer getting enough voltage to provide an adequate spark. Sometimes, you could short across the resistor and increase the voltage to the coil enough to get the engine to start. While he may not have a jumper wire with him, he could take a coin and reach under the dash and short across the terminals of the resistor.

Some actually installed a relay under the dash of their Old Ford that was energized by the starter solenoid. The relay was wired to automatically short across the ignition resistor while the engine was cranking thus providing full voltage to the coil.

You can use a generic "6 Volt" Coil that is designed to be used without a ballast resistor but you would loose any advantage to having the coil operate at its design voltage during the time the battery voltage is low while cranking the engine. However, "Modern" coils are more efficent and the "cold start" feature of the ballast resistor may become less important. Definately Do Not use a ballast resister a with an aftermarket coil (designed to be used without a ballast resistor) or you may get into as situation where your car will be hard to start.

I hope I was not too "Long Winded" in my explination of why Ford used a resistor in the ignition circuits of early V-8s.

Thanks for your patience.

Chris