Who is correct if a high spike line on an oscilloscope indicates a disconnected or open plug wire?

In the context of diagnosing ignition systems with an oscilloscope, a high spike typically indicates that there is a significant voltage present, which can occur under normal operating conditions, such as when the ignition system is firing correctly. When dealing with a disconnected or open plug wire, the expected oscilloscope pattern would not show that high voltage spike because the electrical current cannot complete the circuit due to the open connection. Instead, the oscilloscope would show a much lower voltage level or erratic signals since the ignition coil is unable to deliver spark due to the missing connection.

Given this understanding, if a high spike line is observed on the oscilloscope, it suggests that the ignition system is functioning properly rather than indicating an open circuit. Therefore, neither technician could accurately claim that the presence of a high spike indicates a disconnected plug wire.

This means the correct answer is that neither technician is correct regarding the interpretation of the oscilloscope reading in this specific case.