Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Disconnect the harness from main PCB to display PCB

Measurement:

Measure the resistance of the user control harness.
(from one to the other in turn)
Expect continuity/zero resistance on all tests.
Also visually check the condition of the harness.