Tool Aid SG 23900 Hands Free In-Line Ignition Spark Tester Connects in-line between the spark plug and the ignition wire Use to quickly troubleshoot ignition system with "hands-free" operation Technician can visually check condition of ignition system at each cylinder Frequency and intensity of flash indicates whether there is an ignition system problem or a fault in the fuel delivery system The bright light can be seen in the bright sunlight