A light switch timer fits into the wall, like a regular light switch, and controls all the connected light automatically. You can set the timer to turn the light on and off at any time during 24 hours. Once installed, however, you might experience the occasional problem of an inactive timer.
Confirm that the timer has been programmed correctly, if it fails to turn on. If it's a regular switch timer with a knob and an "On/Off" lever, clear the settings back to zero first. Flip the switch to "On" and wait for the red indicator light to illuminate. Twist the knob to the desired start time and then press it in. The connected light should illuminate, indicating that the start time has been set. Twist the dial to the desired off time and press it in once more. The connected light turns off. You can set as many start and stop times as you like within the limits of the dial times.
If the timer activates the connected light at the wrong times, reset the current time configuration of the wall switch. Move the lever on the wall switch timer to the "Off/Clear" position to clear the previous settings and then move the lever to the "On" position. Twist the knob as close to the current time as possible and push the knob in to save the setting.
The schedule might not work, because the timer is in manual mode. When the light switch is in manual mode, the settings are disabled and the connected light can only be activated with a push to the knob. If the light switch timer features an indicator light, the light remains off while in manual mode. If the indicator light is illuminated, the timer schedule is activated.
If the timer doesn't activate the connected light, it might be working but the light bulb in the fixture might be burnt out. Get on a sturdy ladder and twist the bulb fully into the socket. Turn the light on manually via the switch timer. If the light still fails to turn on, the light bulb might be burnt out. Replace the bulb with a new one.
Unscrew the screws from the light switch timer and loosen the timer and the plate from the wall. Confirm that all wiring is secure and correct. Unscrew the twist connectors and confirm that all wires are stripped of insulation about half an inch and are completely touching. Screw the twist connectors back onto the wires.