Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the 3 pin plug from the fan

Measurement:

Check for continuity (zero resistance) between the ends of the blue and brown wires running to the fan.
Inspect the harness connectors for good condition, check that the insulation is not damaged and that the harness is in good overall condition.