Circuit Control is the application and removal of power. A circuit control diagram can also be expressed as turning a circuit on and off or opening and closing a circuit. As shown in the diagram, control circuits can be divided into major types: two-wire control circuits and three-wire control circuits. A two-wire control circuit can be a simple switch that makes or breaks a connection to a machine. A control circuit is a special type of circuit used to control the operation of a completely separate power circuit. A circuit control diagram shows a combination switch which is the electronic switch assembly that controls several functions.