willysmjeeps.com

OK to use new 6 volt coil i have on hand for my 12 volt system?

From the 1920's to 40's ignition coils were commonly 6 volt as were most electrical systems. As the 12V systems began to appear thru the 40's and 50's the need for more coil power did not occur. So the manufacturers just added a ballast resistor to most firewalls and continued with the 6 volt coil. By the late 50's/early 60's we had what appeared to be 12V coils enter the market. In reality they were still the original 6V coils but now they had internal/integral ballast resistors. Coils did not change much from the 1920's thru the 1970's but then came new type high energy ignition systems and computer controls and finally coils started taking new shapes and new internal construction.

So if you truly have an original pre-1970's 6 volt coil then to use it with your 12V jeep you will need the same ballast resistor used on the 12V CJ5's from the mid 50's on.

thank you thats what i will do .Is there different mfg of ballast resistors? Do they mount on firewall?

Is there different mfg of ballast resistors?

Yes , but just order one to fit a 12V 58 CJ5 PN 938987.

Do they mount on firewall?

Yes

thank you .Al Halliday. Nova Scotia Canada

With most of the stuff we have for our old jeeps, they are dirty and well used and labels have disappeared. I have found that most coils give you some clues.
Unfortunately not consistently applied, but many later coils have embossed on the bottom of the coil can their resistor status. For example, one of my coils states "For Use With External Resistor" on the bottom of the coil. Another older coil I have has a large "6V" embossed on the bottom. Also check the plastic or Bakelite tops of the coils. Many have small notations there like "12V" integrally molded in.
I give coils a good wipe down and external inspection for these clues.
It's a good place to start when trying to figure out what you have, and whether a resistor needs to be employed.
Cheers

I got a 12 volt jeep from “Bubba”.

It has a 12 volt coil. And a resistor on the firewall.....