74 nova circuit gauge

mine is a lil messed up. When ever I turn the headlights on, the fuel gauge goes to empty (I could've just filled it up). I opened it up back there and found that the left side, just before it goes over the center "hump", was a loose. I guess it isn't grounding or something cuz when I pushed it down, the fuel gauge would come back to normal. How can I make it tighter? Would duct tape mess up the circuitry? Thanks.