How to Replace a Light Switch With a Timer

Written by chris deziel Google
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How to Replace a Light Switch With a Timer
Putting lights on timers is a good way to save energy. (kitchen timer image by Inger Anne Hulbækdal from

If you, or anyone in your house, are in the habit of leaving the lights on, you are probably wasting more energy than you need to. A remedy for forgetfulness is to install a timer in place of the switch for any light that you regularly leave on when you don't need it. You can buy digital timers or simple rotary ones that will fit in the same electrical box where the switch is located. Retrofitting a timer for a switch takes only a few minutes.

Skill level:
Moderately Easy

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Things you need

  • Screwdriver
  • Voltage tester
  • Pliers
  • 2 wire caps

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  1. 1

    Turn off the power to the circuit by flipping off the breaker that controls it in the main panel. If you don't know which breaker to turn off, turn on the switch and turn off the breakers one by one until the light goes off. Leave that breaker off.

  2. 2

    Unscrew the cover plate from the light switch and remove it, then unscrew the switch from the electrical box with a screwdriver. Pull the switch out of the box. It has two black wires attached. One leads to the lights and the other comes from the live circuit. You'll have to know which is which, so turn off the switch and turn on the breaker. Test both wires with a voltage tester, placing the red lead on a terminal and the black lead on the ground screw on the switch. The tester will light up when you touch the terminal connected to the live circuit.

  3. 3

    Turn off the breaker, label the live wire and disconnect the black wires and the ground wire from the switch. Straighten the ends of the wires with pliers.

  4. 4

    Examine the wires on the back of a timer switch. They may be black and red or they may both be black. Consult the timer instructions to determine which of the wires to connect to the live circuit and which to connect to the lights.

  5. 5

    Twist the appropriate wire together with the black wire from the live circuit with pliers and screw on a wire cap. In the same way, twist the other wire together with the black wire that leads to the lights and cap them. Hook the bare ground wire around the ground screw and tighten it with a screwdriver. Leave the white wires in the electrical box as they are.

  6. 6

    Push the wires into the electrical box and screw the timer onto the box using the screws that came with the timer. Screw on the cover plate that came with the timer, then turn the power on and test it.

Tips and warnings

  • You can program some to turn the lights on as well as off. Consult the specifications sheet that came with the timer for programming instructions.
  • A timer is useful for controlling a ventilation fan in the bathroom.
  • Be sure to turn the power off before making connections. If you touch a live terminal, you can get an uncomfortable and possibly dangerous shock.

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