When troubleshooting a defective switch, follow these steps: - Turn off the power at the circuit breaker and remove the switch's cover plate. - Test each terminal using a voltage tester. - Ensure the wires are all securely connected to their terminals - If wires are loose or disconnected, resecure them, replace the cover plate, and turn the power back on at the breaker. Try turning the switch back on. - If the switch still doesn’t work, repeat steps 1 through 3. - Once you have reached the end of step 3, disconnect the black wires and twist them together. Connect them using a wire connector.  - Turn the power back on at the breaker.  - The switch is likely faulty if your light comes on and needs replacing.