Hi, I want to install a fan/light fixture in our bathroom. At the moment there is a single pole switch with only one wire from the panel to the switch then to the existing light. The white wire goes from the old light fixture back to the panel to complete the circuit. How do I wire a dual control switch to the new fan/light and the switch for the existing light ? The house was built in '55 and the ground wire is a bare copper wire connected to the metal box the existing switch is in and clamped to the cold water line.