Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the plug from X2 on the PCB and the plug from the Aqua flow sensor

Measurement:

Measure the resistance of each of the wires in the harness to the Aqua sensor from connector X2.
Expect continuity / zero resistance on each wire.
Also visually inspect the harness for good general condition.