The Lisle Corporation Inline Spark Tester with Coil-on-Plug Wire, No. 20580, is designed to give a visual check of spark energy for coil-on-plug or standard ignition systems. Simply connect the tool between the spark plug and the plug wire. The short wire is double ended to offer a straight boot and a 90-degree boot on one tool. With the engine running, the tool flashes a mirror image of the ignition spark. The additional 7” extension plug wire is used on coil-on-plugs that are recessed and hard-to-reach.