Wiring a 12-volt toggle switch involves cutting the wire that powers the accessory and attaching either end to the terminals of the switch. When the toggle switch has three terminals, make sure one of the wires attaches to the center terminal and the second to either of the two remaining terminals.
Before beginning installation of a toggle switch or other electronic component on a 12-volt system, the individual should disconnect the power from the system. For most automobiles, the easiest way to accomplish this is by disconnecting the battery terminal. Once the power is disconnected, installers should consult the vehicle's wiring diagram to determine the appropriate wire for installing the switch.
When replacing a toggle switch, vehicle owners sometimes encounter switches with four wires. On these switches, two terminal screws are one color and the remaining two another. Mark the wires before removing them from the old switch to determine which pairs of wires to match to the same color screws.
In many cases, the existing wires are too short to reach the location of the new switch. Twist-on wire nuts allow splicing additional lengths of wires to the existing ones. Twist the exposed wire in a clockwise direction, and then place the wire nut over the twisted wire, turning clockwise to secure the connection.