pull the sending unit wire off at the tank & with key on should read E then ground this wire to the frame(be SURE you're on bare metal) with key on & gauge should read F if does both of these OK then either the sending unit lost it's ground(common) or the sending unit in the tank went bad. If didn't pass these (2)tests holler back. PS I actually prefer to run a long wire up to the batt NEG post for the 2nd test to be ABSOLUTELY SURE I am getting a ground for a valid test & I only keep it grounded for a second or two just long enough to see if the gauge needle starts moving fast toward F. might not be important but I do not like to peg meters.Grab a helper to watch the gauge inside while you do the connecting.