Looks like the wires were crossed and the ground worked, glad to see it was something simple. As for the guages not working when you switch between tanks, that is because the way it is wired also. The originat switch in the truck is designed for one guage to give a reading for whichever tank you are using. My guess it the install of the second gauge is not working properly because the gauge is not directly wired to the second tank. I would bet that if you switch between tanks the gauge on the left should reflect the gas you have in the other tank. When you switch between tanks, does the guage on the left go down?