High-voltage Detector Mst-880 Spark Plug Tester MST 880 Automotive Spark Plug Tester Tool Mst880 Car Park Plug Tester The product is a high-voltage detector, so when the detectors are not in use, be sure to take the battery out to avoid danger. If the discontinuous state appears in the process of using, that is normal, please loosen the switch with 3 seconds, you can continue to use. In automobile ignition system, the high-voltage ignition coil generates a high-voltage (10,000 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. Place the spark plug on the pedestal Press the key switch, the red LED will illuminate and the good spark plug will generate a strong spark and the bad will generate a faint one or not .