Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN15 from the main PCB
Remove connector CN4 from the display PCB

Measurement:

Measure the resistance between the blue and red wires running from CN4 on the display PCB to the corresponding wire at CN15 on the main PCB.
Continuity (zero resistance) should be measured on both wires.
Also visually inspect the harness for general condition and any signs of damaged insulation.