I work on a lot of 60-66 chev pickups. I assume the ign wiring is similar.
There was a resistor wire taped up inside of the original starter wire harness. That's the wire that feeds the coil when the car starts and you let go of the key to stop cranking.
Then there was a "jumper" wire coming up from the "I" terminal on the solenoid, that hooks to the + side of the coil.
That jumper gives full voltage when starting, and then the resistor wire takes over after it starts.
I put an AutoWire in a 60 P/Up. There was no resistor wire or external resistor (in the new kit) like the 50's chevys had. So, I wired in a external ceramic resistor in the wire that goes from "IGN" on the ign switch, and goes to the + side of the coil. Then I put a solid non-resistor wire from the "I" terminal on the solenoid connected to the + side of the coil.