Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Gain access to both PCBs
Disconnect X1 from the display PCB and X11 from the main PCB

Measurement:

Check for continuity (zero resistance) between the purple, white, orange and red wires running from X1 on the display PCB to the corresponding wire at X11 on the main PCB.
Inspect the harness and plugs for good overall condition.