When you flip the switch on your wall you expect the light to turn on or the device to operate. With a light switch, your first step in checking for a fault is checking the light bulb. When this fails, or the wall switch controls a device like a garbage disposal, you will need to determine if the switch itself is functional.
The first step in testing wall switches is turning the power off at the circuit breaker or fuse box. It is a good step for safety and you may also find your problem right there. If the circuit has tripped or the fuse has blown, repair that problem first. If you still have a non-working wall switch, you will then need to get a multi-meter or continuity checker.
Single pole switches
A single pole switch should have two wire connections and a ground wire depending on the age. The two wires will either be black or a black and white, but the white wire should be coated or covered in black, as it is really also a “hot wire”. Place your test probes on the screw contacts of the switch. In one position you should receive an open or no contact reading, in the other position you should read closed or full continuity.
To replace the switch, loosen the screws that hold the wires in place and reattach them to your new replacement switch making sure that the ground is connected to the ground position, normally a green screw. Use the same type of switch. Replace the switch in the receptacle and replace the cover plate. Turn the power back on and see if your light or device now works.
As a note, white – neutral wires are connected together and should be in the back of the box. A switch only connects to hot lines and ground.
Three way switches
Three way switches are used to turn lights or devices on and off from two locations. They will have an additional red wire that is also called a traveler. When testing a three way switch attach your meter probe or continuity checker to the common wire screw, it should be marked, and leave it there. Attach your other probe end to one of the other two screws on the switch body.
You should obtain an open reading in one switch position and a closed reading in the other position. Now move your probe end to the other screw on the switch body, you should receive an opposite reading when flipping the switch from the first screw you tested.
When replacing a three way switch, it is extremely important to mark your wires before removing them from the old switch. You must attach the wires in the same position on your new switch or the switch will not operate properly.
Four way switches are added to a three way set to allow the operation of the light or device from a third location. A four way switch will have four screws on the main body and when testing you should receive a closed reading in one switch position and an opening reading in the other.
You may need to test this type of switch two ways, some four way switches make a connection vertically across the switch while others make the connection horizontally. Again it is extremely important to mark your wires and install them the same way you removed them for proper operation.
Dimmer switches are used to adjust the amount of power a light receives. This type of switch functions by increasing or decreasing the amount of resistance the switch provides. You will need to use an Ohm meter to check the resistance function of a dimmer switch. As a note, if the switch is hot – warm to the touch – when it is operating, it is most likely overloaded and it should be replaced with a higher rated switch.
Motion or light sensing switches
Motion or light sensing switches turn a light or device on and off when motion or light is sensed by the receiver. These types of switches can be difficult to trouble shoot as the switch will need to be exposed to light or motion to active them. In most cases the sensor will have failed and replacement will be required. Again make sure to mark the wires as you remove them.
As a reminder make sure to have the power turned off before testing and replacing wall switches. The voltage may not kill you, but it does hurt. Many electricians will also wrap the sides of a switch with electrical tape before reinstalling them in the receptacle. This helps prevent accidental contact with the sides of the box for additional safety.