Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect low voltage plug from fan
Disconnect connector X8 from the PCB

Measurement:

Check for continuity (zero resistance) of the each of the four wires running from the fan plug to the wire of the corresponding colour at connector X8 on the PCB.
Check the harness wires and plugs are in good overall condition.