73 Duster only starts in "run" not start posistion

Check to see if you get these readings on your car. I got them on mine. I'd be curious to see if you read the same on yours !

I disconnected my ignition connector on the steering column from the main wiring harness. I place the ignition switch to the 2nd click (Run position)

Taking a volt ohm meter to make make some continuity checks I made measurement from the Red wire to the IGN1 (Blue) and had no continuity. The new cable showed continuity.

Taking a volt ohm meter to make make some continuity checks I made measurement from the Red wire to the IGN2 (Brown) and had continuity. The new cable showed no continuity.

I think that this is the reason that your car will not start when the key position is placed to start but will start when the key position comes back to run (IGN1)

Get back to me and tell me what your findings are !