How To Use： With the engine off, remove the spark plug wire. Attach a black connector to the spark plug. Insert the metal end of the tester into the spark plug wire. Start the engine. (If the ignition circuit is complete, the bulb will flash.) Specification: Type: Spark Tester Material: Plated shaft Product Size: Approx. 11.3 inches/ 28.8 cm in length Quantity:2 Pcs Application: All Internal & External Combustion Engines, cars, trucks, motorcycles, lawnmowers, chainsaws, trimmers, snow-blowers, generators, etc. Suitable for :For any individual, professional mechanic garage, and auto shop. Package Included： 2Pcs Spark Tester.