Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the 4 way connector from the fan assembly
Remove connector X8 from the PCB

Measurement:

Measure the resistance of each of the wires in the harness.
Expect continuity / zero resistance on each wire.
Also visually inspect the condition of the harness and its connector.