Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
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.