Quote:

The one point that may have been overlooked:

The system is basically designed for full output (and long life)with roughly 9 VDC supply. This is about what you have during cranking, and the ignition switch basically shorts the ballast during said cranking. When it starts, you release the key, the charging system resumes operation, battery voltage comes up to 13-14 VDC, and the ballast is again in series, limiting the current flow (and voltage at coil pos.)

Rick




This is basically the correct answer. It has nothing to do with "cooking the coil." Ferd, GM, or Ma could have easily used a 12V coil like many tractors use without a ballast.

It was done for STARTING

When you go out there, in the North Woods, at oh dark thirty to go to work, January 3rd, and it's below zero, the battery "might" put out 9V cranking. So ALL U.S. manufactures back in the day, used a starting bypass system for a hot spark during cranking.

Then, with engine running, the coil "sees" about that same voltage. It varies from 9-12V actually depending on RPM, points dwell, etc with the system running at nominal 14V