- Quick diagnostic tool: The engine spark test probe is an essential diagnostic tool for engines with spark plugs. It quickly and easily diagnoses ignition problems, engine misfires, outboard engine issues, or fuel delivery system failures. It is useful in home garages as well as professional machine shops and automotive businesses. - Premium materials: The probe features a high-quality plated shaft and an optical housing made from environmentally friendly acetate plastic, with a rubber straight sheath and cable. The materials resist rust and corrosion and perform at high and low temperatures. The double-sided flexible body provides a straight boot, and the internal lamp has a long service life. Length is approximately 28 cm, providing reach for hard to access spark checks. - Easy to use: Determine which cylinder is problematic by connecting the spark plug tool between the spark plug and the plug cable, then starting the engine. When a spark occurs, the inline tester lights up to indicate a spark. For a non start condition, have a helper crank the engine to observe the spark. - Light indicator: The tester shows spark presence and discrepancies. A bright white light indicates a healthy spark; a faint color indicates a weak coil or plug. The unit can be disassembled to access and replace the internal bulb. - Applications and compatibility: Suitable for standard spark plug ignition systems. Use it to diagnose ignition problems in cars, motorcycles, outboard motors, and other equipment with spark plugs. Ideal for both personal use and professional shops.