Set Appliance State:

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

Measurement:

Measure the resistance between:
Pin 1 on connector X9 to pin 1 on LWPS harness.
Pin 2 on connector X9 to pin 4 on LWPS harness.
Pin 3 on connector X9 to pin 2 on LWPS harness.
to the corresponding pins of the low pressure sensor connector.
Expect continuity / zero resistance on each of the wires.
Also visually inspect the harness for good general condition.