Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN5 from the main PCB
Remove the fan DC connector (4 wire) from the fan

Measurement:

Measure the resistance across each of the wires in the harness.
Expect continuity on each of the wires.
Also inspect the condition of the harness visually checking for any signs of damaged insulation.