Turn off the power for the room that you are working in by flipping the breaker switch on your circuit box.
Mark the location where you plan to place the new electric switch. Use a stud finder to ensure no studs are near the location where you plan to install the new switch.
Place a junction box against the location you marked. Use a carpenter's pencil to trace the rectangular shape of the junction box.
Cut out the box you drew with a drywall knife. Cut one line of the rectangle out at a time. Continue cutting around the lines until you have the rectangular shape cut out.
Pull the old electrical wires from the hole you made in the wall, if possible. You might need to use fish tape to grasp the wire and pull it toward the new hole. A slim, curved hook might also allow you to grasp the old wires. Another option is to cut a hole as close to the new backsplash area as possible and then run the wire from the second hole to the first hole you made.
Add new wire if you don't have enough existing wire to finish the switch. You must use the same size of wire, such as 14 gauge, as the old wire. Strip off 1 inch of insulation from the end of the new wire with a utility knife and splice it together with the existing wire. Twist the new and existing wires together. Screw wire nuts onto the area where the old and new wires are twisted together .
Feed the wires through the new junction box. Use the screws that are included with the junction box packaging and a screwdriver to screw the box into place in the hole that you created.
Strip the new wire casing by 6 inches with a utility knife. Remove a half-inch of insulation from each wire end.
Twist the wires around the light switch's screws. The wire should go in the same direction as the screw threads. The plain copper wire should wrap around the green grounding screw. White wires should typically be attached to the silver or light colored screw. Black wires should be wrapped around the brass or dark colored screw.
Screw the light switch to the junction box with the mounting screws that are included in the light switch packaging. Cover the light switch with a face plate. Screw the face plate into place with screws and a screwdriver.