The Stovebolt Site Forums The Shop Area The Electrical Bay Why does my 12 volt ignition coil need an external resistor?

I have a 1951 Chevy truck (series 6400) that was converted to 12 volts.
It has a 2 position (off/on) ignition switch with floor start. I installed a new 12 volt coil with an external ignition resistor. As long as the truck is running I will always get a lower voltage to the coil. Was the ignition resistor intended to be used while the truck engine was running but not used during the starting circuit when starting the truck.
With the off/on switch the resistor will always be in use.
Thank You

It should start with the resistor.

This foot-starter switch was used, however, to give 12v to the coil while cranking.

Because that is how GM designed the 12v ignition system.

With 12 volts to the coil it will draw more current then the points can handle & they will not last very long. The switch on the starter has a small term. on the side that bypasses the resister when the starter is engauged. Like TC says it probably will start ok without the bypass. Some coils have enough resistance built into it that they don't need an external resister. These are for low rpm engines like tractors.

Thanks to everyone!
I know that without the ignition resistor the points take a beating. The starter does not have a solonoid
so there will always be a reduced voltage going to the points, which is good. A lot of the older systems used 12 volts to the coil when the ignition switch was in the start position than when released to the on position the resistor alowed reduced voltage to the coil.
Thanks to everyone for their input.

The switch that goes on top the stomp starter on 55 up models has a term on the side for a bypass. But like you say you may not need it.

As shown in the second post in this thread?

What Wrenchbender is referring to is that your stomp starter should have an extra terminal on the side that goes to the coil. When you push on the foot starter there are two different contacts made. One is the big honker to the starter and the other is this terminal which sends full 12V to coil. They both disconnect upon lifting foot. (you are the solenoid). Then the coil gets reduced volts thru the resistor. A solenoid system, as you know, has the extra spring loaded dash switch position which does the same thing for the coil thru the solenoid. Later on, the resistor was replaced with a specific length of "resistance wire" which has about the same ohmage as the ballast resistor....and then came HEI. The purpose was to save the points and maybe the coil.

Thanks again. I will look tonight for the extra terminal on the push start. The truck is in my yard and it is now 12 degrees. When I was younger I would of been out there last night with a flashlight but not at this point in life.
Thank You All!!

That foot stomp switch that Tim has a link to, is a very common switch.
A lot of the old farm tractors have the same switch. They just operated with a hand pull rod with a lever to "stomp" the switch.
Any parts store should have them.

The 12 volt system allows for more voltage to the ignition while cranking, allowing more spark. You stated that you converted the truck to 12 volts. As stated, the resistor is needed to slow the burn on the points. But it is not necessary to wire that feature into the conversion. The reduced voltage provides enough spark.

I converted my 52 to 12 volts. Replaced the generator with a 12 volt alternator, left the 6 volt foot pedal starter and replaced the coil and capacitor, adding a resistor without a bypass circuit. This was over 50,000 miles ago.