My 71 with a 3.3 and 5speed converted from and automatic. Neither the gas gauge or tach work. The temp gauge works fine. I swapped in my spare instrument cluster and nothing changed. I checked the wires at the coil, everything looks good. I have heard about adding an additional ground to the wires behind the cluster. Would this be tapping into the brown wires and running a wire to a known good ground? Complaint, the wires that pug into the back of the cluster are awfully short. I almost thought about adding more wires to both of these to make it easier to plug the cluster in. I need to get to the gas tank in the trunk to check the sending unit it has been awhile. Thanks for your help.