A single failure in any harness can affect the entire system. Open circuits are broken wires, open connectors, inoperable switches, etc. and are by far the most common of electrical faults.
‘Troubleshooting electrical problems can be a frustrating task, but it does not have to be if you keep a few simple rules in mind: Every circuit needs a power source; most electrical devices require a minimum voltage to function correctly; and all circuits require continuity. Consequently, most electrical problems are caused by low voltage (or no voltage), excessive resistance or a loss of continuity…http://www.aa1car.com/library/tselec.htm’
How to use a tone and trace set to find a break in a wiring harness or a short. It is intended to locate wires on a punch down block or other available source.
Continue to the Next Page and watch this great video: How to find an open circuit or shorted wire the FAST easy way.