Trying to Get Stock Fuel Gauge to Work!!

You see no wires to the fuel gauge because the electrical connection is by way of the Printed Circuit Board which it mounts to. The wire for the gas gauge, which comes from the tank, plugs into this PCB.

You may want to start your troubleshooting by doing the easy stuff first. Put your dash back together, have someone temporarily pull the wire off the sending unit at the tank and ground it. With the key on monitor the gauge to see if it moves. If so the problem is at the tank, if not the problem is up front.