How to Replace a Light Switch

Skill Level: Intermediate | STANLEY Pro Project Guides

There are a number of reasons you might need to replace a switch. The switch might be broken, the light may not come on reliably because the switch is failing or has a loose connection.

Look at the switch you are replacing. If it has two brass screws and a green screw, it’s a simple switch, also called a single-pole, single-throw switch (the drawing above shows the wiring configuration for a single-pole switch). If it has one black and two brass screws and a ground, it’s a three-way switch (a single-pole, double-throw switch). If it has four brass screws and a green screw, it’s a four-way switch. For a three-way switch, mark the wire attached to the black screw, using a bit of tape so that you can be sure to connect this wire to the black screw on the new switch. Because of the complexity of four-way switches, I suggest you call an 

electrician to replace a four-way switch.

Remove the wires from the existing switch one at a time, and connect them to the appropriate terminal of the new switch. The two black wires go to the brass-colored terminal screws, and the bare copper (or green insulated) ground wire goes to the green ground screw on the switch. Fold the wires into the box as described previously, screw the switch to the box, and install the cover plate. Power up the circuit and test.



switchdiagram2

To replace a switch, first cut the power at the breaker and verify that the power is off by observing the light go off when the breaker is shut off. Take off the cover plate, check with a volt-tick to be sure that there is no voltage present, remove the switch mounting screws, and pull the switch out. Test again to be sure the power is off at the switch terminals and in all wires in the box. Sometimes there are two different circuits in a box.

1. Check for Voltage

switch1

Before removing the switch, insert the tip of the tester at the sides of the switch; this checks for a loose wire that may still be connected to power. After pulling the switch out, check for voltage again.


2. A Simple Switch with Connections Made

switch2

The two black wires go to the brass terminals, and the bare copper wire is connected to the ground screw. 


3. Three-Way Switch Wired In

switch3

As marked before from the original switch, one wire (either power in, or the wire to the light fixture) goes to the black terminal, two wires go to the brass screws, and the bare copper wire (not visible here) goes to the ground screw.