Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN2 from the main PCB
Remove connector CN1 from the interface PCB

Measurement:

Measure the resistance of each of the wires listed below from CN2 (main PCB connector) to CN1 (interface PCB connector)
Test 1:
Pin 7 (blue) on CN2 to Pin 2 (blue) on CN1.
Expect continuity.
Test 2:
Pin 8 (brown) on CN2 to Pin 1 (brown) on CN1.
Expect continuity.
Also visually inspect the harness for good general condition and any damaged insulation.