Working with a Ferguson TO20 that was converted to 12v neg ground system. It has an alternator, 12v coil and seems to be wired correctly according to a diagram for 12v systems. This tractor ran fine for a year or so, but this year, it wouldnt fire right up. After rebuilding the carb, checking fuel flow and spark, still would not run, just backfires and pops. Then at the end of the day, I somehow noticed a crack in the top of the coil, which I knew had to be the problem. After replacing it with another 12v coil, and rechecking wiring, we got about 3 hours on it running really well, then it did the same thing to a brand new coil. Could the alternators regulator be bad and letting too much into the primary, or possibly just overheating although the engine does not overheat. I tried getting it to fire back up tonight after the failure to check the output from the alt, but couldnt get it running long enough to do so.