Bulkhead electrical gurus to rescue
Who knows, we all have had Gremlins at times.
MYCUDA....
if you have power on the yellow(might be different for diferent years) wire on the starter relay when the key is in run and or off, that is where you start and back trace till you find the source.
If you disconnect the yellow wire from the starter relay and the starter still runs the relay or the throwout is the failure point.
Lastly if you had a wiring change that added a relay, you might have created a loop that after you turn to start energizes and holds the starter relay on