I can't figure this out either. I put a brand new sending unit in, so its not the sending unit. The gauge was working at one point but I had no lights at all when I bought the truck and took it to a local shop. They were about to get all my lights working, but the fuel gauge hasnt worked since. Not sure what it could be. I have a tester and I tested the orange wire going to the sending unit and I have nothing. Could this be a fuse? I looked on the woring diagram, but it shows the orange wire going from the sending unit to the "Printed circuit circuit connector" What ever that is. I don't see it going to the back of the cluster anywhere.