Temp gauge works backwards

[Wmurphy@whmcontractin]

Hey guys, I have a 51 pick up I just rebuilt. Before I started the rebuild the temp gauge went to hot when the key was turned on and than to the Center of the gauge when warmed up. I checked the temp and it's 180 degrees warm. So when I completed the rebuild I changed both sending units with new units from Mac. It still did the same thing so I reversed the location of the wires on the gauge. No difference. Any advice?