Stumped

just at the stud

the base of the sending unit is grounded and the stud is insulated and with it plugged in it could be from 0 to 5v depending on how high the float is.

unplug the sending unit wire. measure the resistance-ohms between the tip of the stud and the base of the sending unit. it should be around 10ohms if the tank is full and about 100ohms if the tank is empty. or somewhere in between