The Engine Spark Tester Probe is the ideal diagnostic tool for engines with spark plugs to quickly and easily diagnose ignition/engine outboard motor problems or fuel delivery system failures and is a must have tool for any personal, professional mechanic shop and auto shop. Shut off the engine and remove the spark plug coil. Connect the black plastic skin connector of the spark plug tester to the spark plug. Connect the metal end of this spark plug tester to the spark plug coil. Start the engine. If the light is blinking, the ignition wire is intact. Dimensions: 6 1/4" shield/cable, 5" shaft/shade. The shaft is nickel plated, the inner bulb lasts for years, and the clear housing is replaceable. Versatile: For basic troubleshooting of all internal combustion engines, cars, trucks, motorcycles, lawn mowers, chainsaws, trimmers, snow blowers, generators, and more.