Sounds to me like the guages are either not getting power or ground or are not connected to motor. Start by checking the power supply to the guages with the key on 1 of the wires should have 12v I think its the purple if that chwecks out make sure the black wire has a decent earth at most 2 ohms.
The fuel guage sender unit or guage could be faulty take the wire off the sender and if its a single wire short it to ground if 2 wires bridge them out the guage should go to the full position if it doesnt its a wiring or guage issue if it dies then the sender is faulty.