Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect high voltage plug from fan

Measurement:

Test 1:
Measure the resistance between the two pins at the disconnected plug on the fan.
Resistance should be greater than 1M Ohm.
Test 2:
Test between the front most pin (where brown wire was previously plugged into) to a suitable earth point.
Resistance should be greater than 1M Ohm.