In Reply to: Resistor on 8N posted by marvin on February 19, 2017 at 13:08:56:
It's there because of the construction of the square coil. As Jack said, it can not handle the current while the tractor is running. But, you need more current to start the car. The ballast resistor does that, just as Jack said. Forget and leave the key on with the points closed and you will melt the coil, even with the resistor.