No start. I know. Another thread but different issue.

yes, the alternator post and through the fusible link and amp gauge hot at all times. The neutral safety switch has 3 wires, 2 of them are for reverse lamps ( purple I think ). Twist those 2 together and you will have reverse lamps at switch on. the 3rd wire, brown or brown w/yellow tracer effects nothing more than starter relay. If this wire is grounded, the relay works, the starter works, even in drive.
This has zero effect on the ignition circuit though. Most likely cause of sudden death is ballast resistor.
I suppose second suspect guess would be ignition switch. All would seem fine checking around with switch in run yet no power to ignition while switch is in start position. In some cases the coil might throw a single spark as switch moves from 1 position to another.