Ballast resistor wiring

So I'm asking dumb questions here but the run circuit is that from the alternator to positive on the coil (labeled above on the drawing as ignition cranking)? What role does the ballast resistor play in that? I can see that it would control the voltage from the battery when starting, but it doesnt look like it is part of the run circuit. Sorry I'm probably talking gibberish. I think I should probably go and buy a book on this.