Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN8 from the PCB
Disconnect the connector from the water pressure switch

Measurement:

Measure the resistance between pin 4 (black) and pin 6 (brown) on connector CN8 to the corresponding wires on the low water pressure switch harness.
Expect continuity / zero resistance on each of the wires.
Also visually inspect the harness for good general condition.