The basic concept of a triple-gang switch is simply three individual switches stacked on top of one another. The triple-switch is convenient because it only requires a single-gang box instead of a triple-gang box. The switches are mounted one above the other, and the switch activates by moving the button horizontally instead of vertically. A double-gang switch is also available.
The switch-box you will be using will have four black and/or red wires inside. One of the wires is the power feed. It is also called the "hot-wire." The remaining three go to the three light fixtures that the switches will control. They are called "switch-legs." Use the voltage tester to determine the hot wire before turning off the power. It is the only powered wire when the main-breaker is on.
Turn off the main-breaker. Put a piece of tape over it to prevent someone from turning it on.
Strip the three switch-leg wires 1/2 inch from the ends. If the switch has push-in connectors, push the wires into the three slots labeled "load." If it does not have push-in connectors, use the needle-nose pliers to bend the end of the wires into a loop and insert them under the "load" screws. Tighten the screws firmly.
Strip the insulation on the hot-wire 1/2 inch from the end. Look on the "line" side of the switch and see if there are small metal jumpers connecting the three terminals. If there are, push the hot-wire into any of the three "line" slots. If they are not there, cut three 6-inch lengths of wire and strip each end of the wires 1/2 inch.
Use a wire nut to connect the three wires (pigtails) to the hot-wire. Push the open end of the pigtail wires into the three "line" slots. If there are no slots, use the needle-nose pliers as in Step 3, and insert them under the "line" screws. Tighten the screws firmly.
Gently push the wires into the switch-box and secure the switch to the box. Add the cover plate.
Turn on the main breaker and turn on each switch, to verify that they are working properly.