Sorry, I gave you false info, the wire to the coil in a 69 is supposed to be Black - Purple not Black - Pink. It starts as black /pink at the switch and changes to black/purple at the firewall junction block.

Good Idea about the wire piercing circuit tester, next time it doesn't start you could check that wire all the way back to the switch. May have to disconnect the starter and have someone hold the key to start to keep the circuit in start mode rather than run mode if the switch has two individual circuits, one resisted and one full volts, a start and a run, leading to the same wire.

Yes the start power to the coil in a 67 and 68 comes from the starter solenoid, and when the key is in run the power to the coil is from the key through a resistance wire. The 69 only has the power wire from the key. I'm not sure if the ignition switch has an internal resistor for the coil in run mode and no resistor for start mode or if the coil can take full voltage in both. I believe it was about that time non-resistance coils were being used but who knows.