Hi Werner, have checked on the wiring schemantics for your car and the fuel level sensor output runs on slate/green and green/black wires to ECU in engine bay on pins 19 and 20 respectively. This means there is no connection directly from sensor to gauge! It appears the sensor signal is not being received by the ECU and its responding as with empty tank, so maybe check the ECU plug. It's the larger of the two connectors. Note the sensor wires run from rear to engine loom via chassis loom so two more connectors to check. Another check (maybe try this first) on sensor itself could be made near tank after removing fuel pump/sensor connector. There should be a measurable (usually lowish) resistance across the sensor wires. If you measure an open circuit then the complete unit needs replacing.
