Product Description: It can be easily test ignition circuit continuity at each cylinder. Great for troubleshooting any internal combustion engine. Indicator light flashes when circuit is working. Specifications: Material: stainless steel+plastic Color: black Dimensions: 3.9'' boot/cable, 4.9" shaft/light housing Design: nickel Plated shaft, double ended flexible tool offers a straight boot -– Internal bulb lasts for years, but is replaceable through transparent housing. How to use: 1.With engine off,remove spark plug wire. 2.Attach black connector to spark plug. 3.Insert metal end of tester into spark plug wire. 4.Try to start the engine. 5.If ignition circuit is complete,bulb will flash. Package included 2 x Spark Plug Tester