Flathead Ford V8's in the 1940's used a ballast resistor on 6 volt ignition systems. My 47 Mercury had one. There was no bypass system and sometimes the spark would get weak when cranking with a less-than-full charged battery. I've never seen a 6V GM system, positive or negative ground, with a resistor.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!