Fuel Gauge

If gauge shows empty at all times, disconnect tank unit wire in trunk (Cutlass and Toronado use a pink wire, all others are tan). If gauge moves to full, check sending unit and ground connection. If gauge does not move, disconnect body connector at fuse block. If still at empty, replace gauge.
If gauge shows full at all times, check tank ground wire. Disconnect sender and ground sender wire. If gauge moves, check tank sender connections or replace sender. If gauge still shows full, check continuity from gauge to tank. If sender wire has continuity, check printed circuit. If circuit connections are good, replace gauge.
If gauge operates, but is inaccurate, disconnect sending unit wire at tank. Connect a known good unit and ground body to frame. Gauge should move as float is moved. If not, replace gauge. If gauge moves, replace sending unit in tank.