Hy QuestarNLinda, as BillyN said you won't have to provide a separate ground once you install the entire cluster. When you are testing outside the vehicle you will have to provide ground circuits to both the sending unit and the gauge. The gauge functions by the varying "strengths" of the two electromagnets on the back of the gauge unit. When the fuel tank is full one electromagnet is stronger than the other, and your gauge reads full, as the fuel level lowers the strength of one electomagnet diminishes and the reading lowers on the gauge, hope that helps.
