Was this motor firing before the MSD ? I mean with that harness ? From the factory, when you have point ignition, there is a yellow wire coming from the starter and going to the coil + along with the ignition + from the ignition switch. This was to give full 12v while cranking, then once started, the motor ran with the 9v from the resistor wire (ignition from the switch, cloth type wire). When you put the key on (not starting), do you have voltage at that cloth wire ? If there is no voltage there, the trouble is either the ignition switch and/or harness between switch and that wire. It's definitely not your MSD since it obviously works. I'm pretty sure that pink/yellow (cloth) wire of yours only has voltage "while cranking" and no more at "ON" position, thus engine only running with key at "cranking" position. To get proof, run a jumper from the positive battery post to that pink/yellow and crank it. If it stays running, you know that is your problem. Let us know the outcome. Frank.