Need help finding one particular wire...

If I understand what you did?????

You used the "crank" or "start" wire feeding to the start relay to act as an ignition bypass?

You CAN NOT DO THIS unless you put a series diode in the wire leading to the ignition. That's because the ignition -- when running -- will backfeed to the starter relay

It should not be that difficult to trace down the original wire---don't you still have the factory connector coming off the ign switch, in the steering column?

I wired my msd like this and didnt need a diode. It cant backfeed because the key switch disconnects the start wire when its in run position, inside the switch.