If a light switch fails to function, you should replace it. If the switch doesn't have the words On and Off embossed on its body and it's the center switch of three switches that control a single light or receptacle, it's a four-way switch. To replace a four-way switch, follow these steps:
Turn off the power to the switch at the circuit panel or fuse box.
Unscrew and remove the switch plate; then use a voltage tester to make sure that the circuit is dead.
Unscrew the switch from the electrical box and pull it out with the wires still attached.
This switch has at least four screw terminals. It may also have a fifth, ground terminal (green).
Mark the location of the four wires with tape so that you can replace them on the new switch; then remove the wires from the switch.
Alternatively, you may choose to transfer one wire at a time from the old switch to the new switch.
Attach the wires to the corresponding terminals of the new switch.
If the existing switch has a green ground wire, attach it to the green terminal on the new switch or to the electrical box.
Push the new, wired switch back into the electrical box and screw it in place.
Screw on the switch plate and turn on the power.