Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Leave connector in place
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the grey wire (pin 4) on connector marked X20 and a suitable earth.
Approximately 12V DC should be present.