Rocker switches provide a visually pleasing way to switch on and off your electrical circuits. Most rocker switches are designed to fit a rectangular cutout, which is much harder to achieve than simply drilling a hole. Because of how nice they look, the extra work involved can be worth it.
Rocker switches come in either two functions, such as an ON-OFF switch, or three functions such as an ON-OFF-ON switch. For each function, the switch can be either a single pole, or double pole switch. A double pole rocker switch is basically two switches in one so that you can operate two circuits with a single switch. And finally, each switch function can be either ON, OFF, or MOMENTARY operation. MOMENTARY operation means that when your finger is removed from the switch, the switch goes back to the OFF position.
Connections on the back of the rocker switches is usually made using 1/4 inch push-on terminals. An ON-OFF rocker switch will have a terminal to connect to your battery or source, and a second terminal to connect to your load or accessory. An illuminated rocker switch will have an extra terminal to connect either a ground wire or common wire to allow the indicator light to illuminate.
A three terminal rocker will have a terminal to connect your source, and two terminals for the two loads the switch will operate. A double pole rocker switch will have either 4 or 6 terminals on the back.