A coil IS a resistor. The coil made to run on 14 volts, and start on 9 volts - and be wired with no extra "ballast" resistor is what is called a "12 volt" coil by many.
If one coil measures 1.5 ohms across the primaries, that part of it IS a 1.5 ohm resistor, etc., etc.
Historically, in the 1930s-40s, some coils did have an extra resistor built inside the can. Not something you see anymore.
Ignition coils specs (a few)
1992 Subaru 12 volt system breakerless: 2.4 ohms across primaries
NAPA IC-12 Echlin 2.1 ohms primary, 8.9 ohms secondary. For 6 or 12 volt systems
NAPA IC-14 Echlin 3.25 ohms primary resistance (no external resistor used) 12 volt system.
NAPA MPEIC14SB same as IC-14, just cheap Chinese. $18.69
NAPA IC-27 Echlin 2.2 ohms primary, 6.38 ohms secondary, for 6 or 12 volt systems
A500 12 volt 2.6 ohms primary, 9.8 ohms secondary 12 volt systems
Deere 6 volt (as used on 430, 1010) 2.6 ohms prim, 7.12 secondary
Hot Spark brand coil - HS06HEC - HEI, CDI and electronic ignition systems requiring a coil with 0.6 Ohms primary resistance. 11.6 K ohms secondary. For 6 and 12 volt systems
Mallory 29219, 6 and 12 volt system coil - primary 1.4 ohms, secondary 9.8K ohms.
Accel coil for points, 1.4 ohms primary resistance, 9.2 k ohms secondary resistance, 42,000 volts maximum voltage. 6 and 12 volt systems
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Today's Featured Article - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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