Spark plug wires (also called "ignition cables") carry high voltage current from the ignition coil(s) to the spark plugs. On older engines with distributors, the wires run from the distributor cap to the plugs, and come in different lengths to reach the closest and furthest spark plugs. Th...
an open plug wire or coil wire will increase the voltage demands on the coil to the point where it may damage the coil. The only safe way to test for spark is to use a spark plug tester tool.