Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN3 from the PCB
Disconnect DC connector (4 wire) from the fan

Measurement:

Measure the resistance between each of
the wires in the harness.
Red to red
Black to black
Green to green
Blue to blue
Expect continuity/zero resistance on each test.
Also visually inspect the condition of the harness.