Answer:
The answer is Technician A only is correct.
Step-by-step explanation:
From the statement that a brake warning lamp on the dash remains usually on whenever the ignition is on, thus if the wire to the pressure differential switch (usually a part of a combination valve or built into the master cylinder) is unplugged, the dash lamp goes out. This is an indication of a hydraulic brake problem because the wire to the brake switch is disconnected thus causing no reportage. Normally, the brake warning lamp supposed to be on usually except if faulty or wire is disconnected as described above.