Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Unplug connector X401 from the PCB

Measurement:

Measure the continuity between the two blue wires (3 & 4)
Expect continuity / zero resistance.
Also visually inspect the condition of the harness.
Is the resistance as expected and is the harness in good condition ?