Auto Car Spark Plug Tester with Adjustable Double Hole Detector Ignition Plug Analyzer Car Spark Plug Test principle: In automobile ignition system, the high-voltage ignition coil generates a high-voltage (10000 volts or more), and the spark plug diverts it from high -tension ignition coil into the cylinder engine, spark between the spark plug electrodes will ignite the mixture. The Detector could tell the good spark plugs from the bad by the strength of the spark. Car Spark Plug Tester Using Note: 1. Please Turn Off Power before you place spark plug 2. The Spark Plug Tester is a high-voltage detector, so do not touch spark plug with hand at work to avoid danger. The higher the frequency, the stronger the spark strength. Car Spark Plug Tester User Manual: 1.Place the Spark Plug into tester hole 1 or 2; If you want to compare the new spark plug and old one, place new spark plug into hole 1 and the old on into hole 2. 2.Connect to power supply 3.Turn the key switch 4 clockwise to turn on tester, indicator 3 will light up, tester is now working at 1000rpm/min. 4. Again turn the key switch 4 clockwise,you can adjust the working frequency between 1000rpm to 5000rpm/min.