Usage Tips: Troubleshooting: Used to test spark plug performance and troubleshoot internal combustion engine problems. Diagnose ignition/engine outboard problems or fuel delivery system malfunctions quickly, easily and safely. Safe and reliable troubleshooting method, convenient, economical and time-saving. Versatile: The spark tester connects between the spark plug and spark plug wire in seconds, solving problems with dirty connectors, sharp corners, and poor wires or connections. You can quickly and easily diagnose whether your car's drive system is working properly. High-quality material: Made of high-quality PVC plastic, which is resistant to high temperatures, aging, corrosion, and strong insulation. Good materials can extend the service life of the product. Instructions for use: Simply connect the tester between the spark plug and spark plug wire and when a spark occurs, the tester reflects the spark and lights up - look for dirty spark plugs, broken spots, broken wires or connections.