I believe that "yellow" wire in the post #38 diagram should have full battery voltage in the key "start" position ONLY which powers the coil on cranking startup.
In the key "on" position, the "blue" provides the coil with power through the ballast.
In what I read from your post #48, the coil must be seeing power as you allow the key to rotate back to the run (ign 1) position for the engine to catch and stay running.
I'd think I'd trace the "yellow"(ign 2 in post #28) back from ballast Steve.
How I check...…
1) Disconnect both sides of the ballast.
2) Disconnect the ECU plug.
3) Attach volt meter to Ign 2 ballast plug and ground.
Zero volts in "key off" position.
Battery voltage in "key start" position.
Zero volts in "key on" position.
4) Attach volt meter to Ign 1 ballast plug and ground.
Zero volts in "key off" position.
Zero volts in "key start" position.
Battery voltage in "key on" position.
