How do you replace a light switch?

After you obtain a matching type of switch (there are three major types, see below):

  1. Safety: Understand that we all make mistakes or that a new switch may be defective, and be careful. In some circumstances, a mistake or defect can cause an electrical hazard or a fire inside the walls. Check if your fire insurance will cover work done without a license. Check if you need a local permit to do electrical work. Never do electrical work alone.
  2. Turn off the electrical current for that light circuit at the breaker/fuse box. If in doubt, turn off the whole house. Someone may have moved things since the labels were last updated.
  3. Remove the face cover by taking out the screw or screws. Unscrew the top and bottom screws holding the switch.
  4. Pull the old light switch out of the safety box far enough to see the wiring terminals. Verify you have the right type of switch for the replacement (same number of wire terminals).
  5. Use a voltage tester to make sure there is no voltage between any of the wires (and ground, if there is one). Be careful of wires going to other switches in the same box; they may be on a different circuit breaker. To be safe, turn off those circuits too.
  6. Loosen the terminal screws with a screwdriver. If they use spring terminals instead, use a sharp object to press the release hole and then pull out each wire.
  7. Place the new switch next to the old one and move each wire to the same position on the new one. Wrap wires around screws clockwise and tighten each terminal. Note: if one terminal is marked COM on a 3-way, make sure that wire goes to COM on the new 3-way switch. The other two hot wires can go either way.
  8. Replace the new switch into the box, replace the cover, turn on the power. Pay attention if the breaker pops or the fuse blows at this point. If so, you made a mistake. Leave the circuit off, call qualified help.
  9. If power is still on, try the switch. If it is a three-way or four-way circuit, try all combinations from each location to make sure they all work.
  10. If there are sparks or the power goes off again, or the light doesn't work, you made a mistake. Make sure the power is off again, then call someone more qualified to help figure out the problem. Watch for several minutes in case there is smoke or other indications of a bigger problem.

One person wrote: "I am not an electrican---Make a diagram of the wiring. Replace 1 wire at a time. Black (hot)wires go to the brass screws. White wires (neutral) goes to the silver screws. Incoming hot is usually coming up from the bottom. Out going to the fixture is on top." Because installations may vary randomly on which wire goes where, and whether power is top or bottom, it might be better to have a qualified person assist in this task.

Black to brass, white to silver screws holds true for receptacles but not for switches. Switches have two brass screws and can have two black wires on them or a black and a white or even a red wire.

There should not be any "white" wires at a switch. If there are (e.g., because a cable was used), they must have colored tape (not green) wrapped around them to indicate they are NOT neutral. No neutral wires should ever be switched. If there are any wires connected together (e.g., two or more white wires), leave them connected to each other. If there is a bare (or green) grounding wire, make sure it also gets connected the same way it was on the old switch.

You also need to make sure you use the same type of switch as the old one. There are "normal" single-pole, single-throw (SPST) light switches (two screw terminals, plus ground); "three-way" single-pole, double-throw (SPDT, three terminals, plus ground); and "four-way" double-pole, double-throw (DPDT, four terminals, plus ground). The switch may also be of a special type, such as "dimmer" or "lighted", or a special decorator shape that will affect whether you get the same cover back onto it.