Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect connector M4 from the PCB

Measurement:

Test 1:
Measure the resistance between the two inner wires on connector M4.
Resistance should be approximately 40 Ohms.
Test 2:
Measure the resistance between the inner brown wire on M4 to a suitable earth point.
Resistance should be greater than 1M Ohms.