Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X2 from the PCB
Remove connector from the low water pressure switch

Measurement:

Measure the resistance across each of the wires to the low water pressure switch as below.
Pin on connector (X2)Water Pressure Sensor Connector
11 (Black)Black
13 (Red) Red
14 (Green)Green

Expect continuity on each wire in the harness.
Also visually inspect the harness.
Note:
Each pin on the PCB connector is numbered.