A single light switch that controls two fixtures, such as two lights or a light and a bathroom or ceiling fan, can be converted to a double light switch that allows you to operate each fixture independently.
If each fixture has a separate cable running to the switch, this is a fairly simple task. You'll need a screwdriver, a pair of wire strippers, a double switch plate and a voltage tester.
If the fixtures are wired in a series – meaning the switch connects only to one cable and the fixtures are wired to each other inside the wall – an electrician will have to be called to separate the cables and run them individually to the switch.
Ensure All Power Is Off
Wear gloves and rubber soled shoes at all times when working on electrical wiring. Turn off the breaker to the wall switch you will be working on. Remove the wall plate, and use a voltage tester to check for power by touching the end of the detector to the light fixture in several places. If the detector light turns on, then power is still running to the switch.
Remove the Old Switch
Pull the switch assembly carefully out of the switch box until you can see the wires attached to the screws on either side. There should be three or four wires attached to screws on the switch. Take a photo of the switch with the wires in place for reference.
Identify the Switch Wires
The feed is the hot wire that sends electricity to the switch, which determines if the electricity is then sent to the fixture. This live wire is often – but not always – red or black, and is normally attached to the side of the switch that has a small metal tab.
There should be two neutral wires - one for each fixture. These are often – but not always – white. There should also be a grounding wire, which is normally green, yellow or bare copper. Some houses may not have grounding wires, and have been grandfathered in under older building codes.
Disconnect the Wires from Old Switch
Unscrew and detach all of the wires from the old switch. Two wires will probably be wrapped around each other. These are the separate wires for your fixtures. They will need to be carefully separated, and each one wrapped with a small piece of masking tape labeled "A" and "B."
Connect Wires to New Switch
The new switch will have several places to connect wires. The ground wire, if one exists, will go to the screw that is green. Alternately, it will go to a screw in the middle or bottom of the switch. Curl the wire into a clockwise hook, slide it under the screw head and tighten the screw down.
White neutral wires will go to the sides of the new switches without the metal tab. In some cases, neutral wires may be twisted together, secured with a wire nut and pushed into the back of the switch box. (Only follow this method if the original switch was wired this way.) Red or black feed wires will attach to screws on the sides with the metal tab. Attach these in the same manner as you did the grounding wire. Only attach one wire to each terminal.
Cover all terminals with electrical tape to reduce the possibility of electrical shorts. Set the new switch back into the box. Turn the breaker on and test the double switch, noting which switch now controls which fixture. Install the wall plate.
Your single wall switch has now been converted to a double wall switch, so you can control lights independently or turn on a light without turning on a fan and vice versa.