Packard Forum Index » V-8 (1955-56)

HH56 wrote:
That white thing on the firewall is a ballast resistor needed in most 12v systems to lower the voltage to the coil when the engine is running so coil and the points do not overheat. On Packards and many other brand cars, only when the engine is cranking is a straight 12v fed to the coil so the spark will be extra hot for an easier engine start. As soon as the engine starts and starter motor disengages the straight 12v is removed and the resistor then provides an approximately 8 or 9 volts to the coil to keep the engine running. Some brand cars use a specific length of a special type wire for connecting power to the coil instead of going thru a separate resistor and other brand cars have the resistor built into the coil housing.

A loose connection would cause intermittent issues and a constant 4 or 5 v to the coil would definitely cause running problems. Those ballast resistors can burn out or sometimes change value. A common burned out resistor symptom is the engine will start OK on the initial 12v but as soon as the key is released and starter motor quits so does the engine. A resistor that increases value and provides a lower voltage might give the same symptoms you experienced with the loose connection while one that might melt and short a few turns of the resistance wire together to lower the value will increase voltage so the coil or points could overheat and burn...

Pgh Ultramatic wrote:

An important clarification to the above is that the ignition system is not getting 12v during cranking. It's connected to the battery, but the starter is at that time pulling the battery down to 8-9 volts, therefore the ignition system is working on a consistent voltage. It doesn't need "extra" voltage during cranking.