Learning how to wire a light switch is a basic skill every homeowner should know. It takes only a few minutes to complete, and you don’t need specialized tools.
Start by removing the switch from the electrical box to expose all the wires that connect to it. Check each length for signs of damage or fraying, and cut off any degraded sections with wire cutters. Leave about a half inch of exposed wire on each length.
The pliers on your electrician’s toolbox are ideal for this task because they have a nifty feature that lets you insert the wire through a small hole and bend it into a U-shape to fit snugly around the screws on the switch (Images 1 and 2). This creates a tighter connection and keeps the wire from getting damaged in future use.
Once you’ve removed the old switch, disconnect all power to it from the circuit breaker box. This is important because working with electricity is dangerous, and you can’t work on the wires if they are still connected to the switch or fixture.
If you have a one-way switch in place, remove it and carefully identify which wire is connected to COM / C and which runs into L1 on the new switch. Usually, this will be brown or red on older circuits. Alternatively, you may have a 2 way switch in place with traveler screw terminals for the other wire.
Next, wrap the black and white wires around the brass terminal screws on the right side of the switch in a clockwise direction. This will ensure that the connections tighten as you turn the screws.
After you’ve finished wrapping the black and white wires, wrap the copper wire around the green grounding screw in a clockwise direction. You can also use the electrician’s pliers, as they have a nifty feature that allows you to insert the wire through a small hole and then bend it around the lip of the pliers (Images 3 and 4).
Finally, insert the entire configuration into the electrical box, tighten the screw, and then turn on the light to verify the wiring is secure.
Three-Way Wiring: This requires a few more steps than one-way wiring, but it is worth the extra effort because the wires connect all switches to each other so that they will turn on or off independently.
To do this, you’ll need a length of Romex cable that is 14-3 type NM (or 12-3 if it’s a 12-gauge wire). It should have four wires: black, white, ground, and red.
The black wire will carry a live current from the electric panel to the light, while the white and ground wires will connect the switch and fixture. The red wire is a traveler wire that can connect to either a left or right upper terminal on the switch.
Once you’ve completed all the wiring for your new switch, it is time to install it and replace the old cover. You’ll want to make sure the switch is level, and that you don’t over-tighten the screws. You’ll need to attach the cover back to the electrical box, too.