Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect ON/OFF switch plug from PCB (bottom left)
ON/OFF switch set to ON
ON/OFF switch set to ON
Measurement:
Measure the resistance across the black wires of the disconnected plug.
Resistance should be short circuit (zero resistance).
Resistance should be short circuit (zero resistance).
Isolate as per TOPs P4
and refit as necessary