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Switches are used to turn lights or electrical devices on and off. Usually when a switch fails, a light or electrical device will not turn on. After determining that a light bulb is not burned out and a circuit breaker or GFCI is not tripped, the switch may have failed.
This troubleshooting page assumes the switch wiring is correct and switching has worked correctly in the recent past. If you think there is a problem with the wiring or if someone has worked on it but did not fix it, call an electrician.
Troubleshooting a single pole switch is fairly simple.
Check for voltage on switch terminal
Place leads of continuity tester on the two terminals with power off
Notice the burn marks on a failed switch caused by an internal arc flash. If you hear a crackling noise inside the switch, it is caused by internal arcing and is ready to fail.
If a lamp that is plugged to a switched receptacle does not work, it could be a bad light switch. Below is an example of troubleshooting a lamp with a good bulb that does not turn on.
Using an electrical meter, check for power at the switched part of the receptacle, or use a voltage detector to see if there is voltage on the lamp cord.
If there is power present at the receptacle and on the cord, there could be an open circuit in the lamp: