[FlatheadTed]

As far as I know The 12 volt system that came in for cars in the 50s became the std ,some had a visible resistor and some had it in the coil or resistant wiring ,with a by pass to full 12 volt through the ignition key .part of the idea of running a resistor was to give a hotter spark for starting also balance voltage fluctuations ,and to compensate for starter load ,Eg like running 12 volt through a 6 volt bulb it will be bright ! you can do this momentarily on a limited bases .With Fords 4.1/2. volt you get a shot of higher current eg full volts for starting until the resistor heats up then it drops . This is just my take on it .