Truck Won't Run

[HO455]

Originally Posted by Bunkythe3rd

Ok, so if the yellow wire is the 12 volts to the starter, which one is the resistor wire? Is it part of the connector in the back?

Oh also it is a 1969 Chevy C20 by Vin. It has a 67 front end on it.

Think of it this way. The yellow wire is actually 12 volts FROM the starter when it is energized.

As it came from the factory your truck's ignition coil was designed to run on 8 volts. (Approximately thereabouts) That 8 volts was created by supplying 12 volts to the "Resistor wire" (Also commonly referred to as a Ballast wire) from the ignition switch. Just like a resistor in an electronic circuit the "Resistor wire" drops voltage by a certain amount depending on how it was manufactured.

When starting the engine the voltage available from the battery will drop. It can go as low as 9 to 10 volts. When that happens the 8 volts at the coil drops too. It may drop too low to make enough spark to start the engine.

So to solve this condition GM (And many others) added a terminal to the starter to supply 12 volts to the coil when the starter was energized. That wire is the yellow wire on your truck.

That yellow wire and the ballast wire were usually connected at the coil. Not having the "Resistor wire" or a suitable replacement connected to the coil means the coil is only getting power when the starter is energized. Shut the starter off and the coil is no longer powered and the engine dies.

HEI ignitions were designed to use 12 volts so the "Resistor wire" disappeared from GM vehicles at that time.

Hope this helps.