Pinched the wire?
Did you take the sender out of the tank? If so, it may be backwards. The wires come out on the BACK side, pointing towards the rider.
MP
+1, exactly the same problem on my new to me IS. You can unfasten the rear of the tank, lift it up a little, and see if the wire comes out toward the back of the tank. Easy to confirm, a lot harder to fix.
When the sending unit comes out, and you "try" to put it back in correctly, it will be a real "B" to do. That is why it's in there wrong now.