Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect plug from water pressure sensor
Disconnect X7 from the PCB

Measurement:

Check for continuity (zero resistance) across each of the wires running between pins 1, 6 and 8 of X7 to the connector for the water pressure sensor.
Inspect harness and connectors for good overall condition.