If you have to get to the sending unit, why not install an inspection plate, that is if you can determine where it is in relation to the tank cover. I thought my ground wire got severed while running some other wires and the guage quit working so I was prepared to install the insp. cover. Mine has an inspection cover near the front so I took a mirror, flashlight and tape measure to determine the center of the sending unit. (While under there, I found my ground wire and got mine working again.
) Good luck!