Ignition Coil Troubleshooting

[Christopher R.]

My '62 wouldn't re-start after a long hot drive. The car was towed home. After a few days rest, I tried to start it. No luck. Not even a cough. Changed the coil, and it started instantly. Sounds like a bad coil, right?

Tested the suspect coil today. The primary resistance between the (+) and (-) terminals is 1.2 ohms. The secondary resistance between the coil tower and the (+) terminal is 10.57K ohms. Both of these numbers are within typical values.

So, is the coil bad?

[Dave S.]

Re: Ignition Coil Troubleshooting

My '62 wouldn't re-start after a long hot drive. The car was towed home. After a few days rest, I tried to start it. No luck. Not even a cough. Changed the coil, and it started instantly. Sounds like a bad coil, right?

Tested the suspect coil today. The primary resistance between the (+) and (-) terminals is 1.2 ohms. The secondary resistance between the coil tower and the (+) terminal is 10.57K ohms. Both of these numbers are within typical values.


So, is the coil bad?

Chris,
The only way to thoroughly test a coil is on a running car. If the coil is fully heated up and it does not work then it is no good. Not repairable either.

[Richard M.]

Re: Ignition Coil Troubleshooting

Since it still failed later after cool down, and after you swapped it out, now good, maybe there was a bad connection somewhere. Maybe in the process of changing it, you unknowingly fixed a connection issue.

I'd carefully check the Green wire from Ballast to coil+, as well as the Black coil- to distributor.

Another possible issue is the Black wire inside the distributor connecting the points breaker plate to ground.

I'd do a retest. Start it will the present config with new coil. Shut down. Install the suspect coil and try to restart. I suspect it will since it meets spec. Let it warm up to normal temp.

As Dave said, coils typically fail when hot, but since it still failed cold , something else may be a issue.

Maybe even Ign power from Ign switch. A test light or meter can help find that if no-start. Meter the coil+ to verify 12v first.

Rich