It surely has to be right there. The wiring mess, shorted / crossed wiring, or a bad switch.
YOU HAVE TWO sources of igntiion voltage.
1...With the key in "run" the IGN1 terminal sends power out through the bulkhead, normally dark blue, to the ballast, the voltage regulator, and depending on year, to other loads under the hood, such as electric choke, if used. THIS GOES DEAD when cranking to start.
2...With the key in "start" a second set of contacts, IGN2 comes alive. This is normally brown, feeds out through the bulkhead, and connects to the ballast at the coil side. It's purpose is to provide "full battery voltage" during cranking to the coil
Bear in mind that if you have EVER had some sort of short that heated up part of a harness, the insulation can melt in there and you can get, uh, "interesting" cross connections. I would start at the switch. If you unplug the switch, and the engine dies, you have found it. Otherwise, there is something in the harness. Also bear in mind that by moving/ wiggling the harness, if it has a cross, that you may have temporarily fixed the problem. Yeh, I know. intermittents suck