A-1 HOW TO READ THE WIRING DIAGRAMS PDF fileHOW TO READ THE WIRING DIAGRAMS - How to Read Circuit Diagrams A-5 Indicates input/output to/from controlunit(currentflowdirection). Input Output Input/ output In case two or more connectors are connectedtothesamedevice,markings indicating the same connectors are connected by a broken line. Indicates current flow downward or upwardascontrolledbythecontrolunit. Wiring Diagram - Read and Draw Wiring Diagrams Recognize Wiring Diagram Symbols. To read a wiring diagram, first, you have to know what fundamental elements are included in a wiring diagram, and which pictorial symbols are used to represent them. The common elements in a wiring diagram are ground, power supply, wire and connection, output devices, switches, resistors, logic gate, lights, etc.