Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove both ends of the fan harness, from the plug at the fan end and from X8 on the PCB at the back of the lowered facia
Remove both ends of the fan harness, from the plug at the fan end and from X8 on the PCB at the back of the lowered facia
Measurement:
Measure the resistance of each of the 3 wires (black, orange and green) of the harness.
Isolate as per TOPs P4
and refit as necessary