Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect plug from fan

Measurement:

Measure the resistance of each of the wires on connector X5 at the display PCB (Pins 1, 2, 5 and 6) to the wire of corresponding colour at the fan connector.
Expect continuity / zero resistance on each test.
Also visually inspect the condition of the harness and its connectors.