If the engine can emit spark, the tester bulb reflects the spark and lights up, so as to quickly find the fault point and bad circuit of the spark plug.
Spark Plug Diagnostic Tool Spark Plug Tester Simple Spark Plug Tester for
25069 Adjustable Ignition Spark Tester, Spark Plug Tester for Small Engines and
Practical Plug Engine Ignition Tester Inline Spark Plug Tester for Automotive
