1. 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 for any personal, professional machine store and automotive store2. Turn the engine off and remove the spark plug coil. Connect the black plastic leather 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 flashes, the ignition wire is intact.3. Size: 6 1/4" shield/cable, 5" shaft/light cover. Shaft is nickel plated, internal bulb lasts for years, clear housing is replaceable4. Wide range of uses: for basic troubleshooting of all internal combustion engines, cars, trucks, motorcycles, lawn mowers, chain saws, trimmers, snow blowers, generators, etc.5. LYHLYA aim to provide good products and services for our customers. We have good and reasonable return policies. Feel free to contact us if you need any help or have any question, we will be very happy to give you a satisfied solution in time.