In Reply to: Re: Ford 2N Ignition Coil Circuit posted by Phillip G. on August 09, 2022 at 15:30:41:
Factory 6v (runs about 7.2 charging) had a coil ranging from about 1.0 to 1.5 Ohms (not real tight tolerances) and a dash mounted 3 terminal block containing a temperature dependent resistor that was around 0.3 Ohms room temp & 1.3 to maybe 1.7 RED HOT, and typically running conditions was about 0.5 Ohms. So, 7.2/(1+0.5)=4.8A and if coil 1.5 Ohms, 7.2/2.0=3.6A. The temperature dependent function allowed for some limiting/adjustment/variation/etc. Now, if converted to 12v system (running 14.4v) and keep 6v coil, dash mounted resistor, then current would be 14.4/(1.0+0.5)=9.6A... killing such coil! So along comes the white ceramic resistor of anything from 1.0, 1.2, 1.3, 1.4, 1.6, 1.8, and some even as high as 2.5 Ohms. Makes these a gamble unless you know what you have either by part number or good accurate measurement.
Let us look at 1.3 & the 0.5 dash & the 1.0 coil. 14.4/(1.3+0.5+1.0)=5.1A. Up the ceramic to 1.6 & then 14.4/(1.6+0.5+1.0)=4.6A. And if coil is 1.5, then 14.4/)1.6+0.5+1.5)=4A. So, here we are in ball park of original system currents.
Before each cylinder had its own coil many/most cars & trucks ran about 14.4/3.25=4.4A, but those round can metal coils were more robust than the front mount coils and no doubt better quality insulation construction than today's Chinese imports.
If use a "12v advertised" front mount coil of 2.5 Ohms, your current will be too high, at 14.4/2.5)=5.76A, so most conversions leave the dash mounted #12250 resistor in place and end up with a current of about 14.4/(2.5+0.5)=4.8A.
If whatever you are using works well, I would leave it alone and file all this where ever you like. If is ain't broke don't fix it!