I recently purchased a 1975 k5 with factory a/c. I cannot manually select anything but off. When I move the controls, nothing happens. I have pulled the controls out and all the vacuum tubes look in good shape, but there is a orange wire on the back that is disconnected. Does anyone know where this wire is supposed to go? Also, my blazer has a gauge cluster that has a tach where the fuel gauge is on most blazers. Is this tach a factory option or is it aftermarket? It has three wires on the back that are disconnected. They are black, pink, and brown. Any ideas where they go? thanks.