Making a double light switch from a single light switch allows you to add an additional switch without tearing up your wall. Utilising the existing electrical box eliminates the need for a larger electrical box. If your single light switch is currently operating two light fixtures, you can add a double light switch to allow those lights to operate separately. That will save energy by not using power in an area where the lights or another electric device isn't needed.
Disconnect the power to the switch by turning off the breaker that feeds the location.
Remove the switch plate cover. Unscrew the two screws that hold the cover to the switch.
Disconnect the switch. Remove the two screws that hold the switch to the electrical box. Pull the switch from the box. Loosen the two screws on the side of the switch to remove the wires. One screw will have two black wires connected to it. These two wires connect directly to your light fixtures. Label these two wires with black electrical tape.
Cut two 8-inch pigtails from 14 gauge THHN solid black wire. Strip 1/2 inch of insulation off of each end of each pigtail.
Connect the two pigtails to the black wire you did not label. This wire connects directly to the circuit breaker. Twist an orange wire nut onto the three black wires, connecting them together.
Connect the new single pole double switch to the fixtures. This switch fits in the same space as the switch you removed but has two separate switches. One switch sits on top of the other, and they act independently. Connect one of the wires you labelled with black electrical tape to the top black screw on the right side of the switch and tighten the screw. Connect the other wire you label with black tape to the bottom black screw on the right side and tighten.
Connect the pigtails to the new single-pole double switch. Connect one of the black pigtails to the top copper screw on the left side of the switch and tighten the screw. Connect the other black pigtail to the bottom copper screw on the left side of the switch and tighten. Push all the wires into the electrical box.
Attach the new single-pole double switch to the electrical box. The switch attaches with two screws at the top and the bottom of the switch.
Cover the switch and the electrical box with a receptacle cover. The cover connects with one screw to the centre of the switch.
Turn the power on at the breaker panel.
When you work with electricity, make sure the power is off to the location at which you are working.