To install a two-way electrical switch, disconnect the power supply to the switch line, prepare the installation location and the power supply wires, and attach the wires to the switch. Reconnecting the power supply and testing the switch completes this process.
Start by gathering a screwdriver, a wire cutter, a wire stripper and a current tester. To avoid possible electrocution, disconnect the power supply to the switch line you intend to connect the switch, and put a notice at the junction box so that someone else does not reconnect the power. To prepare the installation location, unscrew the faceplate from the switch installation location with the screwdriver, and unscrew the old switch from the switch box. Test the wires attached to the old switch for any current with the current tester. Then, unscrew the wires from the switch, and remove the switch.
Once the installation location is ready, prepare the wires by removing insulation from their ends with the wire strippers, taking care not to remove too much insulation to avoid a possible electrical short after the installation. If needed, cut the wire ends to suitable lengths with the wire cutter. To attach the wires to the switch, connect the black and white wires from the switch box to their respective corresponding wires in the new switch. Finally, connect the red wire to the point where the black wire originates, reconnect the power supply at the junction box and remove the notice.