its going to be one of the following
loose cable (unlikely), just cry rather than replace.
knackered needle (half half), if the needle never moves then this is going to be the most likely cause. Undo part of the dash and replace the clocks
knackered sender on the pump (ding ding ding), my favourite in this category, remove rear seat bench, disconnect battery, open all doors, crack the tank open and replace the pump.
Let others have there say first as