Coil question

zeke57 · Post by **zeke57** » Sun May 03, 2020 5:06 pm

When using an electronic distributor is it ok just to use a standard coil? I tried to start my a1 last night but it would not fire. I did have it running a few months ago with the same ignition system in place and it ran fine. So I got out the multimeter to check the coil and I had a reading of 2.9 ohms on the primary side and from what I have read it should be between 1.2 and 1.8. The secondary side is reading around 8,500 ohms. This coil was new so I am wondering if it being used in conjunction with the electronic distributor could cause it to fail or did I just get a bad coil.

Post by **wesk** » Sun May 03, 2020 7:38 pm

When using an electronic distributor is it ok just to use a standard coil?

I will assume here that you are referring to a simple hall effect electrical switching device that replaces the function of a set of mechanical contacts and not a full blown "Electronic" ignition system that varies spark automatically based on sensor readings for manifold pressure, RPM, fuel mixture, and vehicle speeds.

The Pertronics pointless replacement system as well as the M151's later pointless systems made no change to coils.

I had a reading of 2.9 ohms on the primary side and from what I have read it should be between 1.2 and 1.8. The secondary side is reading around 8,500 ohms. This coil was new so I am wondering if it being used in conjunction with the electronic distributor could cause it to fail or did I just get a bad coil.

You got a bad coil coil or a cheap overseas unit.

The preferred method of testing coils in the Army was by checking amperage draw under load. That takes a very complicated test setup. So the second choice is Ohms.

zeke57 · Post by **zeke57** » Sun May 03, 2020 8:24 pm

Thanks Wes I knew after taking the readings the coil was bad I just wanted to make sure that I did not need a special coil to use with the electronic distributor. So coil shopping I go. Anyone have a more reliable brand they like more than others?

Post by **wesk** » Sun May 03, 2020 8:43 pm

I believe you will find only two choices: offshore repops and US Built NOS. The NOS are getting rare as hen's teeth. One of our members modified a modern high energy automotive 12 volt coil for the task to fit inside the military distributor.

http://www.willysmjeeps.com/v2/modules. ... sc&start=0

zeke57 · Post by **zeke57** » Mon May 04, 2020 6:49 am

I forgot to mention that I did a 12v conversion sorry about that. I read an old post on this forum from July of 2018 in which Wes mentions that the Prestolite 200691 was the coil used on the f134 for years and there is a place in LA that supposedly has them so it got me to wondering if this is a NOS coil from back in the day would it still be good even though it has sat for years or are the 200691's still being produced?

Post by **wesk** » Mon May 04, 2020 8:18 am

If you have a 12V conversion and a civvy distributor then just use a brand new 12 V coil that would be used in an 70's or 80's auto. They will come with internal resistor requiring no external ballast resistor on the firewall like the old CJ's used. The original CJ 12V coil was 933160 and it's resistor was 938987. Here's an example of what's available today in 12V (Built in resistor) modern coils:.

https://www.kaiserwillys.com/replacemen ... EvEALw_wcB

https://www.completetractor.com/new-12- ... lsrc=aw.ds

jnissen · Post by **jnissen** » Tue May 12, 2020 1:02 pm

Hopefully you resolved this. For the 12V we settled on about 2.8ohms of primary resistance (combined coil and ballast resistor). Starts instantly. The electronic ignition module we are using recommended the primary resistance be 3 ohms minimum but it's working just fine. If you use a internally ballasted coil most of them measure out about 3-4 ohms.