Usage: Test spark plug performance and ignition strength Application Range: 12V Gasoline vehicles car spark plugs Widely Application: 100V-240V input voltage. JF109 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 form high-tension ignition coil into the cylinder engine, spark between the spark plug electrodes will ignite the mixture. The JF109 could tell the good spark plugs from the bad by the strength of the spark. 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. JF109 Spark Plug Tester User Manual: 1. Place the Spark Plug into tester hole 1 or 2; If you want to compare the spark plug and old one, place 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 6000rpm/min.The higher the frequency, the stronger the spark strength. Note: Installation guide not included, we strongly recommend you seek professional installation. Please check as much as possible to make sure the item is what you need. Tips:The product may be updated constantly,Due To Different Batches, The Actual Product May Have Slight Differences Or Color Differences, Which Does Not Affect Use. Plug Type:US Plug, it applies to Canada, India, Mexico, Thailand, Taiwan, the United States, the Philippines and so on. Voltage:AC110V Colour:As Shown Material:Plastic Package Contents: 1 x JFIND