BDRCobra,
The wires that are zip tied to the filler neck are used for Reverse Lights, if required.
The fuel tank sender wires should be top center, if you look underneath and straight up where the fuel outlet pipe is. I have looked in the trunk and I think it would be underneath the battery tray area. I don't know if an access hole is there or not. I haven't searched that deeply.
My fuel gauge readings will vary as I accelerate and deaccelerate also. I have the Stainless steel tank with baffles.
Just a note on the fuel gauge readings when I first filled my SS tank up in this old thread:
Fuel capacity