Starter stays engaged ONLY in park???

I got screwed up in the edit. Try this:

Double check, with everything connected normally. Engine stopped. Put shifter in anything except park or neutral Put key in "run."

Probe ballast terminals and confirm: One end of ballast should show close to 12V and other end should show quite low, perhaps 6-8V

Now probe the yellow wire at the relay and see if there is any reading there for voltage.
I don't have a yellow wire going to the relay, are you referring to the wire going to the ignition terminal? I'll post a picture soon.

Disregard, I see you called it the start circuit earlier.