Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect mains voltage plug from fan (3 pin connector)

Measurement:

Measure the resistance of the brown and blue running from the disconnected plug to X3 on the PCB.
Brown = X3 Pin 1
Blue = X3 Pin 2.
Inspect harness and connectors for good overall condition.