Ok. Made a bit of progress.

Undid the hack job of wiring. Found a melted fusible link, fixed it to how I think it goes. I still need a wiring diagram.

Wired how it looks like it goes, the truck runs even better. No need for the toggle switch haha.

Got the truck to fire up with the key, got the radio working (after swapping to a different/better radio)

Only thing now is the gas gauge does not work now.

Also is throwing code 12 (battery disconnected within last 50 key cycles) still and code 15 (no vehicle speed/distance input) which I'm betting is the non functioning speedometer. It is cable driven, and the head was zip tied together. I'm hoping that a new cable fixes it.

I never thought I'd be messing with a TBI truck