Usage:
Reference: Understanding Causes Of Blown Fuses And Tripped Circuit Breakers and How To Troubleshoot A Short-To-Ground In Power Wiring in this issue.
SIMS and claims comments are very helpful in diagnosing failure modes of electrical components. "Shorted, open and intermittent" can often be used to quickly and easily identify the condition of a component that is not performing correctly. These terms are often misunderstood. Correct understanding of these terms aids correct reporting of component problems and speeds the problem cause/resolution process.
An "open" is an electrical circuit that will not conduct current, a broken path for electron flow. It is sometimes described as "infinite" or many ohms.
Examples: Blown fuse or tripped circuit breaker, head lamp switch in "off" position, engine that will not crank because of corroded battery connection, dead wiper motor because of poor ground to cab, EMS oil pressure switch with dead engine, or dead hour meter because engine oil pressure switch did not close during operation.
A "short" is a direct electrical connection between two points, usually very low resistance or opposition to current flow. It most often describes an unwanted or incorrect connection and may draw higher than expected current.
Examples: Dead forward warning horn causing blown fuses/breakers, head lamp switch that will not turn lights off, engine oil pressure switch that will not turn off hour meter, pinched harness causing blown fuses (or tripped circuit breakers), or a start switch that keeps the starter engaged.
An "intermittent" is an unwanted and erratic event that occurs in a normal or correctly-operating circuit. It most often causes a closed circuit (one that is "on") to open up or turn "off." It can also take place in a powered circuit (+12 or +24V, etc.) where it might be connected to ground and blows a fuse or trips a circuit breaker.
Examples of an "intermittent open": Vehicle tail lights that sometimes blink "off," EMS oil pressure LED that sometimes blinks "on" during normal operation when pressure has been confirmed to be within specifications, when one or both gear indicator LED's blink "off" on transmission controls, or a loose screw on a head light housing causes the light to blink.
Examples of an "intermittent short": A turn signal switch in the "off" position that continues to flash the lights, or start-aid push button that will not release (open) and causes ether solenoid to burn out (often "shorts" and blows the fuse/breaker), or wire-to-wire harness connection (short) where application of brake lights also turns "on" tail lights.
Examples of an "intermittent short-to-ground": Where a third LED turns "on" in a given gear on the transmission control, when a fan or wiper motor burns out (shorts) and blows a fuse or trips a circuit breaker, when a powered wire is pinched to ground and blows a fuse/breaker, when a screw driver is used to ground a circuit to see if it is "hot". These conditions in power wiring often cause permanent damage to other components like switches, fuses, and circuit breakers.