To expand on this a little more, starting around 1960 GM had the bypass wire coming off the starter solenoid. There was a terminal mark " S " and one marked " I " on the solenoid. The " I " was for IGNITION, it supplied full battery voltage to the coil when the solenoid was pulled in while the starter was cranking. Once the engine started and the key was returned to RUN, battery voltage dropped off the bypass wire, and the coil used the resistor wire for voltage supplied by the key switch.
When electronic ignition came out in 1973, GM used the key switch to send power to the coil in the start mode doing away with the bypass and resistor wire.
The 1954 version used an upstream resistor, and a single wire to the coil with a second wire spliced in right after the resistor. In start mode, the key would apply battery voltage to the coil wire via the spliced in wire after the resistor, once it started, the battery voltage dropped off the spliced in wire and the voltage came through the resistor and out to the coil by way of the key switch run position. 1953 and prior used a single wire to the coil.
I went through the wire diagrams here,
https://chevy.oldcarmanualproject.com/electrical/wiring/ it looks like 1954 was when they started using the bypass wires and resistors with variations of how they switched between them. Prior to '54, they were all wired using battery voltage from key switch to what must have been a coil with resistors built into them. By 1960 they settled on the starter solenoid / key switch method and stayed with it till '73.
If I got something wrong, feel free to point it out, I will change or delete so its accurate.
