Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the large 20 way connector (ST9) from the right hand side of the PCB.

Measurement:

Measure the resistance between pin 9 on the disconnected connector at the PCB to a suitable earth point.
Resistance should be OL
Note :
Colour of the wires may vary but the terminal position will remain the same.