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

Measurement:

Measure the resistance of the blue and red wires running from the disconnected plug to X1 on the PCB.
Red = X1 Pin 1
Blue = X1 Pin 2.
Inspect harness and connectors for good overall condition.