Originally Posted by
9-3 Aero
The reply based on the 9-5 wagon, as MY of car in question is not given.
Measure the fuel sensor voltage at the disconnected fuel pump and sending unit connector, pin #4, positive 12V or a little less, depending on the internal resistance of the multimeter, and pin #3, gnd. A (good) voltage reading here indicates unbroken contact towards the Main Instrument Unit (MIU).
Measure resistance of the sensor: Empty tank: 40+/-1,5 ohm, full tank 250+/- 6,5 ohm.
Grounding the signal wire may not have been a good idea, as the input circuit of the MIU normally has a minimum resistance.