After putting in a new Autometer Tach into my '68 Camaro the Gas gauge now reads way past full. I discounted the tach and the gas gauge still goes way past full. So I read through the past postings and grounded the brown wire that plugs into the sending unit, which is in the trunk, but the gas gauge did not go to empty as it should have. I looked for a ground wire behind the Speedometer and Fuel gauge assembly and all I find is a single connector that contains a bunch of wires. Is the ground wire in the bunch? What is/are my next steps to determine where the failure is?