A three way switch allows one appliance to be controlled by two switches. This kind of switch works by opening and closing circuits. If one switch is turned on, the other cannot be used. This is because an open switch will disrupt the flow of electricity to the appliance. This structure is often used for controlling a light situated on top of a stairway so that it can be switched on from the top and bottom of the stairs. Other appliances can also be controlled using this kind of switch.
Be sure to cut the power to the area before working. Measure the distance from the first switch to the second and mark where it will go.
Obtain a pop-in box to house the wires inside the wall. Trace the front of the box on the wall where the switch will be placed. Mark the box and cut a hole for it. Drill a hole on the ceiling directly above the place for the box so that you can run your wires. The holes should be able to hold two to three wires going downward.
Trace the wire coming from the switch to the light. Once found, remove the wire from the switch. Drop the wire to the new switch. Do not forget to untwist all wires when removing the switch.
Tag or mark the wire coming from the light so that you can identify them later. Take the box out from the original switch. Since you have electricity going to your switch, you only have to run two wires from there to the site for the second switch. See to it that you will be able to tag both ends of one of the two new wires. This will be your link that will connect both so that you can activate the light from any of the two.
With wires at both sites, strip the wire exposing 6–8 inches of the three different wires inside. This should be enough to enter and exit the box. Put the wires into the box at the new site and secure it into position. Twist the individual black and white wires going from switch to switch. Hold the individual black wire coming from the light and twirl around the other two coiled wires.
Wind the exposed wires together. Then push them to the back of the box where the wire cap is placed. Coil the two “white neutrals” together and push them back into the back of the box. Remove the cap so that you can place and replace them after you are done. Put a wire cap on the black wire that is left and then push back.
Go to the other box and strip the wire. Reinstate and firmly fix the box back in the wall. Coil the marked wire together, and then coil black individual wires together. Coil a single strand of black with those two and let it stick out 3-4 inches for the switch to connect. Uncover and link all other wires this way. You should not have a single black wire left over. Install switches accordingly.