A few tests have to be made before a root cause can be determined. With the sending unit float arm in the empty stop position, resistance should be 15 ohms (below E). With the sending unit float arm in the full stop position, resistance should be 160 ohms (above F). The fuel gauge should read empty at 22.5 ohms and full at 145 ohms. These tests will isolate whether your concern is a sending unit wiring or a gauge.