Fuel sending units read WRONG time after time!

You get the readings you want with the instrument cluster out of the dash, but when you put the cluster back in the readings go nuts, right??? Well, OK then. Normally your gauge cluster is grounded to the car body by contact with the metal in the dash and by the screws that hold it there. With the cluster hanging by its wiring you have NO GROUND, and whatever readings you're getting are bogus! Hook up a ground wire from a metal part of the dash to the ground trace of the instrument cluster and start over. When you have no dedicated ground path (either with the cluster installed or with a dedicated ground wire referenced previously) the voltage supplied to the cluster will find some kind of path to ground through the other circuitry, producing the bogus readings you're getting. GOTTA have a good solid ground path!!

BC