This is an example of electrical wiring diagram representing a mechanical function. The vertical dotted lines on the forward and backward buttons show that the normally closed contact and the normally open contact are connected. So, pressing the button will open one set of contacts and close another set. A wiring diagram is a graphical depiction of the components and cables that comprise an electrical connection. Wiring diagrams are widely used in circuit design and other electronic device tasks. The layout promotes communication between electrical engineers who design and install electrical circuits. A wiring diagram is very important in vehicle maintenance and house construction projects.