Finding electrical shorts

Posted on December 1, 2001

It can be frustrating and time-consuming to locate a short in an electrical system, especially in a school bus, which has seemingly miles of wiring. But David Ruth of Wolfington Body Co. in Exton, Pa., says there’s no need to panic. With these tips, which he provided in the Pennsylvania School Bus Report (Nov. 2001), he says you will be able to locate the majority of electrical shorts with little headache. 1. Use a test light, a digital volt/ohm meter or a continuity tester. 2. When possible, have schematic diagrams on hand of the circuits you’re dealing with. 3. Don’t jump to conclusions and start replacing electrical components, such as circuit breakers, switches and relays, without investigating. 4. Locate the beginning and end of the circuit where the short is located. Check traditional problem areas, such as bus body intersections where wiring makes a 90-degree turn or is routed around a sharp edge. 5. When dealing with lighting systems, try removing a blown fuse and installing a circuit breaker of equal amperage in its place. Chances are the short is located where any lights are out or dim. 6. Try removing a dome light or speaker from the wiring trough above the passenger windows and cutting a wire halfway down the length of the bus to pinpoint the location of a short. 7. In most bus bodies, there are junction plugs that can be disconnected to isolate a short. 8. Remove a wire from a component, such as a switch or relay, and momentarily apply 12 volts to that wire. If you get a heavy blue arc, you most likely have a short to ground.

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