Weird problem with starter today. Opinons welcomed!

Don't fool yourself unless you want to feel like a fool.
The starter doesn't get power unless the starter relay sends it there.
Some problems don't require a lot of technical info to diagnose. I never will forget the ford Bronco that went across a Bi-Lo parking lot (without hitting anything) and tried its damnest to climb a bank until the battery died. Stuck closed starter solenoid.
You have a large wire on one side of the relay that goes to the starter. Disconnect it. Now cycle the switch over and over again and see if you can recreate a stuck relay or a faulty ignition switch.
If not, you may have wires to the starter melted together by the headers. As a service tech for several years, I learned that basic understanding, logical thinking, along with close visual inspection got them out in the streets again much faster than reading. Too many times over the years, a simple test light showed me where the fault was.