The spark tester is used when performing an engine mechanics test using a cylinder pressure transducer. In this case, the plug wire of the cylinder under test is connected to the spark gap.
Please note that in cases where additional high-voltage equipment such as an adapter for plug wire extension or a spark tester is used, you should always carefully check the electrical connections in the high-voltage circuit and at the points of connection to the vehicle ground.
The spark tester uses a spark plug with an interference suppression resistor to suppress radio interference.