It is possible you have 2 unrelated faults.The fuel gauge may be a fault with the gauge driver Pcb which is screwed to back of gauge.(I have recently repaired one of these cos it can only be bought with the gauge).As for the other dead instruments ,have you checked the fuses?Some time ago we had a 405 with half the dash dead & it turned out to be a blown fuse!! yea 2 fuses for the gauges-it can only be a French car!!