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 interface PCB

Measurement:

Test 1:
Measure the resistance between pin 1 (Red) and pin 3 (Blue) on connector CN2.
Expect approximately 108 ohms
Test 2:
Measure the resistance between pin 2 (Black) and pin 4 (Brown) on connector CN2.
Expect approximately 225 ohms.
Test 3:
Measure the resistance between each of the wires on connector CN2 and earth in turn.
Expect open circuit on each test.