Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Continuity Set meter to measure Continuity
Disconnect the 4 way connector from the PCB and fan

Measurement:

Check the harness leads for continuity.
Measure between either end of the disconnected connector to check the continuity of each of the wires in the harness.
Green to Green
Blue to Blue
Black to Black
Brown to Brown
Check the general lead condition.
Reconnect harness after test.