No power on “cranking” cycle from key-73 Dart

If you have a multi meter that has the little buzzer sound to test continuity, you can unplug the harness from the neutral safety switch and clip your meter onto each side of the wire. If there's continuity, you'll hear the buzzer sounding. Then shake the wire around and see if the buzzer cuts out. If it does, then you have a break in the wire that will give you intermittent problems.

Odds are more likely in favor of the NSS being bad.