Not sure when farmall went to a coil, my 1950 farmall C has a mag. So the old mags don't have a ballast by-pass circuit. A by-pass circuit shorts out the ballast resistor when starter is cranking. This applies the full battery voltage, minus a few volts, because the battery cranking voltage is usually less than 12v. This is how all the old cars were wired back in my day. The ign switch was responsible for applying full voltage to coil when starting.
I used a diode to apply 12 volts to coil when the starter is on. I connected the anode to the starter wire, the cathode to the + coil wire. Some starter solenoids have a terminal for this purpose, mine didn't. For me, the diode was the simplest way to get the job done.
Sometimes I think 12v conversion is spinning the starter too fast. I slowed my farmall C down by using a 185 cca lawn mower battery. I like the way it starts turning over slower. Just my opinion, but I think the old tractor were designed to start using a crank, lot slower than even a 6v battery. I hand started my share of old tractors and kick started old motorcycles. Nothing fast about that.
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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
... [Read Article]
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