A switch assembly is a device used to turn a mechanism on or off. Offered in one of several designs, a switch assembly can be found in push/pull, momentary or toggle versions. The common switch assembly is designed to work with an electrical charge to activate a response in a device, though pneumatic, magnetic and optical style switches are also available for use in a wide variety of functions.
Most types of switches are designed to either break or connect an electrical circuit. When the switch assembly is in the closed position, the circuit is complete and current is able to flow through the switch. Conversely, when the switch is in the open or off position, current is unable to bridge the gap created by the open switch, thus, the current is unable to continue through the circuit. While many switches are wired into the positive electrical current, some are wired into the ground side of the electric circuit. With a pneumatic switch assembly, the air is permitted to flow through the switch when it is in the closed position and is restricted when the switch is open.
Components of a typical electrical switch assembly include the contacts, terminals and a switching mechanism. The contacts are the components within the switch body that are bridged or opened to allow or deny electrical current to flow through the switch. Terminals are the exterior components that are attached to the wiring harness to hold the switch in position within the harness, and also provide a location for electricity to enter and exit the switch body. Switching mechanisms can vary from a simple toggle device that is flipped back and forth to a push button that can either be depressed to connect, such as a starter switch, or to disconnect, such as a kill switch.
Switches are available in a variety of designs, from the simple off or on type of switch that is completely open or closed, to a rheostat-type switch that can offer a wide array of settings from partially on to completely on, such as a volume switch or the burner control on an electric range. Tilt switches, also called mercury switches, use a metallic liquid to complete a circuit when the switch body reaches a certain angle. This type of switch assembly is often used to turn on a service light under an automobile hood. When the hood is opened a certain amount, the switch sends power to the under-hood light, turning it on. Once the hood is closed and the switch is placed in another angle, the light is turned off.