Do the same test, but do it by shorting out the points with a screwdriver (instead of while cranking). Very simple test. If you then get good spark everytime you jump them, the points aren't making/breaking as they should.
In you still don't get good spark, check voltage at the primary terminal of the coil. Anything over 7 volts should be more then enough. If very low, check your resistor.
As far as the coils goes, in most cases a "12 volt" ooil used with a resistor IS a "6 volt coil". OEM IH or Deere 6 volt coil is 2.6 ohms on the primary and 7 ohms on the secondary. Standard 12 volt coil can be 1.92 to 2 ohms on primary and 6-9 ohms on the secondary. My point being a 12 volt coil made to be used with a resistor is NOT made to run on 12 volts. It is basically the same as a 6 volt coil to run wiht no resistor.
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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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