Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove the 12 way connector from the front of the PCB

Measurement:

Test 1:
Measure the resistance between pin 1 (black) and
pin 2 (blue) on the 12 way connector.
Expected resistance approximately 4 kOhms.
Test 2:
Measure the resistance between pin 1 (black) and a suitable earth.
Resistance should be greater than 1MOhm (or O.L)