[Clint72]

And so it continues, I just realized that my passenger head ALSO has a sending unit in it.
It appears to be a light switch rather than gauge.
It has a green with white stripe wire running to it.
From all of my looking at wiring diagrams, I'm 90% sure these trucks didn't have both it was one of the other.

Edit:

Ah I've gotten closer!!
I looked up a 73-87 engine wiring diagram and it matches some of the wires I had being unused in my engine bay!