Set Appliance State:

Mains Power Off
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 inline connector to check the continuity of each of the wires in the harness, blue, green, black and brown
Check the general lead condition.