Features: Automobile spark plug test principle: In automotive ignition systems, high voltage ignition coils generate high voltages (above 10,000 volts), The spark plug transfers it from the high voltage ignition coil into the cylinder engine, between the sparks The spark plug electrode will ignite the mixture. The detector can distinguish the strength of the spark from a good plug from a bad plug in the following ways. Precautions for the use of automotive spark plug tester: 1. Please turn off the power before placing the spark plug 2. The spark plug tester is a high-voltage detector. Do not touch the spark plug with your hands during work to avoid danger. The higher the frequency, the stronger the spark strength. Auto Spark Plug Tester User Manual: 1. Put the spark plug into test hole 1 or 2; if you want to compare the new spark plug with the old spark plug, please Insert the new spark plug into hole 1 and the old spark plug into hole 2 2. Connect the power 3. Turn the key switch 4 clockwise to turn on the tester, the indicator light 3 is on, and the tester works at 1000rpm/min. 4. Turn the key switch 4 clockwise again to adjust the working frequency between 1000rpm and 5000rpm/min. Specification: Name: Spark Plug Tester Material: ABS + Metal Plug: US Plug Power adapter input: 100-240VAC Package Included: 1 x Spark Plug Tester