Coil compatability

[Danny Phillips]

This one is for michael mayben I think. Michael I just blew up the coil while driving today and she stopped dead in the road. 74 Scout II, 345 with IH holly points type dizzy and some hokey micronta cdi ignition that when you push the button on top it won't start at all, its an on off button, 727, Dana 20 with Dana 44 w/ front discs. My question is, I have a spare 345 with a prestolite electronic ign. Can I use the coil from the prestolite on a points type dizzy? My plan is to freshen up the spare and swap engines. Thanks michael.

 

[Michael Mayben]

this one is for michael mayben I think. Michael I just blew up the coil while driving today and she stopped dead in the road. 74 Scout II, 345 with IH holly points type dizzy and some hokey micronta cdi ignition that when you push the button on top it won't start at all, its an on off button, 727, Dana 20 with Dana 44 w/ front discs. My question is, I have a spare 345 with a prestolite electronic ign. Can I use the coil from the prestolite on a points type dizzy? My plan is to freshen up the spare and swap engines. Thanks michael.

That "micronta" cd box is a radio shack item from about 25 years ago! I never actually ran one but they were kinda "popular" based upon the smokeblow in the old radio shack big catalogs they used to distribute back then (not at all like the stuff they do today).

Yes...the specifications (primary and secondary resistance values) for the coil used oem with breaker points, the Holley gold box electronic system, and the prestolite electronic system (and the prestolite points distributor) are all the same for the sv engine apps...a primary resistance range of 1.4>1.8 ohms is perfect.

However...with that cd box, I'm pretty sure the oem "resistance" wire feed to the coil positive terminal when the key switch is is "run" position was eliminated in the hookup (or at least it should have been!). If you are going to bypass/eliminate the micronta unit, then the ignition primary side needs to be wired back like it was originally...that means b+ feed to coil positive in the key switch "start" position, and either the oem resistance wire, or an aftermarket ballast resistor with a value of 1.2>1.8 ohms needs to be wired in, but not both types of "resistance" components.

I'm basing my comments on typical installations of add-on cd ignition boxes such as msd, accel, mallory, crane, etc.

Great question! Ya just never know what kinda aftermarket add-on stuff ya might find on this old iron! This is what makes this stuff so interesting to me...that the gadgets have actually survived all these years (to a degree!).

 

[Danny Phillips]

Thanks for the reply michael. If I get rid of the cdi can I just install a ballast resistor and hook it to switched b+.

 

[Michael Mayben]

thanks for the reply michael. If I get rid of the cdi can I just install a ballast resistor and hook it to switched b+.

Exactly!

The "universal" ballast resistors I use are standard motor parts #ru 10. Those are a nominal 1.8>2.0 ohm items and work perfectly with the coil specs I posted! Always test a ballast resistor for determining it's actual value when cold.