Open and Shorted Circuits

Open and short circuit diagram.

Open Circuits: An open can occur anywhere in an electrical circuit. There is no current; it's just like turning the switch off. When there's an undesired open in a circuit, the component the circuit controls will not function. There will be no operation. This is often caused by a blown fuse, an open circuit breaker, or a broken wire. If an electrical component has no operation, the fuse box is a great place to start.

Short Circuits: Shorts are caused by unwanted current flow in a circuit. Excessive current flow will result in a blown fuse. This may be caused by an undesired path to ground, or by two wires crossing each other. This results in two different circuits shorted together and excessive current flow in the circuit. These touching wires can cause strange behavior in a vehicle. One circuit may activate the other. For instance, the horn may blow when the turn signal was intended.

A vehicle’s ground is the engine, chassis, or frame. A short to ground occurs when an unwanted flow of electrons is directed to ground before the circuits desired load. Check for a frayed wire touching the vehicle’s dash, frame, or engine allowing much of the current to flow to ground instead of the desired system component. Inspect for any screws or holes drilled through the firewall near the wire harness, damaging insulation and crossing wires.