OK Scotty, heres what I can add here...
The stud with no nut in the picture is one stud of 2 holding the gas guage into the cluster. The circuit board pin that corresponds with the stud with no nut is the dark blue wire in the round plug cluster. The other stud with the nut from the gas guage shares the circuit board with the voltage limiter thingy mounted on the back, but doesn't appear to go to the round cluster plug. I believe the limiter side is sending power to each guage, and the side connected to the cluster plug is the "meter" side. Blue goes to the gas tanks sending unit, and I'll bet if you look at the color of the wire going to the tank, it's blue.
Hard to do without a wiring diagram, and if I had one for 64-65 I would gladly share, but it's pretty easy to figure out the wiring in these early A's, especially with the diagram!! I have an extra cluster and harness here if you need reference, and I have a WD for 1966 to refer to also!! Maybe Del will chime here also!! Hope this helps, Geof