I did want to point out one thing many dont know. Up until about 1973 GM and Ford also used resistance in their point ign systems. But they both used a resistance wire in the cars wire harness that drops the current flow thru the ign circuit just like Mopars ballast did. Mopars ballast resister changes with temp of course as when the car is idling and the dist turns slowly the points are closed longer so it would heat up some and have more resistance but at higher rpm when the dist turns faster the points are not closed as much and the ballast cools a bit and has less resistance for a slightly higher coil output at higher rpm. I believe the GM and Ford resistance wire works with heating up and cooling also just like Mopars ballast. If you look at an older wireing pages on the GM and Ford point ign you will see the resistance wire in the ign primary circuit. Thats why both Ford and GM have the resister bypass circuit on their starter solenoids to bypass the resistance when cranking just like Mopar does with the ign switch. Ford did use a resistance wire at first like Mopar with its electronic ign but stopped using it later and GM did not use it when they went to their HEI in 1973. Ron