Set Appliance State:

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

Measurement:

Test 1.
Measure for resistance across pins 1 (brown) and 2 (blue) of connector X3.
Expected resistance greater than 1MΩ (or O.L).
Test 2.
Measure for resistance across pins 1 (brown) and 3 (green/yellow) connector X3
Expected resistance greater than 1MΩ (or O.L).
Note:
Pins may be multicoloured.