Larry is absolutely correct and here are some diagrams.
This is the stock wiring used on most all the years from early 60s to early 70s including the 72.
The stock factory wiring showing the starter wiring and the stock points coil with the resistance wire. The yellow wire is for the starting cycle to give the coil a full 12 volts for starting. After ignition and engine running it drops out and the ignition voltage runs through the resistance wire to fire the coil during normal operation. This is to protect the coil from over voltage burnout.
Here's the resistance wire from the fire wall connector. This is a very good place to run the HEI distributor power from, since it comes directly from the key just like stock. It requires removing the stock resistor wire from the block and installing a new wire from the block to the distributor.
This is a picture of the actual wire in the block. It started as a white orange purple wire but over time it gets to looking like a cloth covered white wire like in the picture. The large purple wire next to it is the solenoid S terminal wire.
I believe the red and green wires on the starter were just power wires to some other devices.
Here is the diagram with the HEI wire installed.
