Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove X3 connector from the PCB

Measurement:

Test 1. Measure for resistance across pins 6 (Brown) and pin 7 (Blue)
of X3 connector.
Expected resistance Greater than 1 MOhm.
Test 2. Measure for resistance across pin 6 (Brown) and Earth
(Main terminal block).
Expected resistance Open Circuit.
Test 3. Measure for resistance across pin 7 (Blue) and Earth
(Main terminal block).
Expected resistance Open Circuit.