I was working on my 54 today and had key on for about 15 or 20 minutes. I went to cut key off and noticed coil (12 volts) was hot as a firecracker. I felt of the rest of the wiring (new original wiring harness) and it was not hot under the hood or inside truck What would cause the coil to get that hot with just the key on. Have it hooked up correct I think ignition side to plus side and distributor lead to minus side. Thanks

 

Normal. When the key is on and the points closed you have constant current flow through the coil. Check your points, they may be burned. Leaving the key on is a no no.

 

What he said, I've seen coils fail after being left on also.

 

The key is "the points are closed". Of course there's no way for you to know that with the cap on.

I did the same thing once on my Harley. Instead of a few minutes, mine was on for days. The coil was shot.

Hopefully, you caught yours in time to save the coil.

 

Going to argue with you, Joe. If you are real observant, the amp meter will show slight discharge when the points are closed. All is good and meant well. I know that you know that.

 

Actually, I had forgotten that, so it's a good thing to mention. Unfortunately in my case with the Harley, I have no meter to show charge/discharge.

But you're right about our trucks.

 

I was told a long time ago that if you have a ballast resistor in the system, the resistor will heat up when the key is left on with the points closed. The resistance increases with heat and will eventually reduce the voltage to the coil to the point where it generally won't be damaged. It will still kill the battery after some time has passed.

As usual, all generalitys are false....so it probably won't work that way every time.

Dan

 

That's what I was taught way back when, as far as the resistance being temperature-sensitive. Supposed to reduce voltage at idle speeds, more than at higher speeds.

 

Didn't the Mopars use those a lot?

 

The current draw will be higher without the engine running, that's for certain.

 

Mopars used "that" style, the porcelain block. Since these are easy to mount the Mopar design was real common on a 12 v conversion.

Ford used a ballast resistor wire for the ignition 56 up. Not sure what GM used.