Find and turn off the circuit breaker that feeds the existing switch. Remove the switch plate and the two screws that secure the switch to the wall box. Carefully pull the switch out of the box by pulling on the top and bottom tabs. Do NOT touch the side terminals on the switch until you are sure the circuit is off.
Use the voltage tester to make sure the power is off to the circuit. Loosen the terminals and remove the wires. Disconnect the ground wire from the switch as well if it has one connected to it.
Use the stud finder to determine on which side of the switch box the stud is located. Hold the old work box up to the existing box, open face to open face, so that the corners line up on the side where the stud is located. Trace around the old work box with a pencil. Use the drywall saw to cut away the extra drywall so the new box will fit.
Label the wires with some tape so you know which wires are the feed wires and which ones go to the fixture(s).
Remove the existing wall box. If it was originally installed when the house was built, it will be nailed to the stud. That will make it difficult to remove. You can try hammering it out or breaking it apart with a hammer and chisel. Just be careful that you don't damage the wires when removing the old box.
Run a length of NM cable from the location of the switch box to whatever the new switch will be controlling (light, fan or outlet). Make your connections at that final destination.
Insert all of the wires from the previous box and the new cable line into the double-gang switch box and install it inside the wall. Tightening the screws will engage the tabs that keep the box secure.
Cut and remove the outer sheath of the new cable using a Romex stripper. Then, use the wire strippers to strip a 3/4 inch of insulation away from the ends of the new wire. Check the old wire to see if it needs to be re-stripped as well. Group all of the white wires together and connect them together under one wire connector. Wrap the connection with electrical tape, and push the wires back into the wall box.
Take two 8-inch lengths of spare black wire from the NM cable and strip 3/4 of an inch of insulation from each end. Connect the two wires with the black feed line using a wire connector. This will give you two feed lines branching off from the original one. Wrap electrical tape around the wire connection.
Connect all of the ground wires together with two ground wires branching out from the wire connector. Connect one ground wire to the ground screw on one switch and the other wire to the other switch's ground screw.
Connect one feed branch to the bottom screw on one switch and the other branch wire to the bottom screw on the other switch. Connect the original fixture wire to the top screw on one of the switches. Connect the black wire from the new line to the top screw on the second switch.
Wrap the terminals on both switches with electrical tape, secure the switches to the wall box and install the double-gang switch plate. Turn the circuit breaker back on and test the installation of the extra wall switch.
Things You Will Need
- Voltage tester
- Wire strippers
- Drywall saw
- Stud finder
- Romex stripper
- Double-gang old work box
- Double-gang switch plate
- Single-pole light switch
- Electrical tape
- Wire connectors
- If you're adding an extra wall switch to control additional lights using the same circuit (as we described here), make sure the circuit can handle the additional load.