Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Summer/Winter Switch in Winter position
Disconnect wires from the Summer / Winter switch noting their positions

Measurement:

Measure resistance across the top and bottom spade connectors which the wires were previously connected to.
Resistance should be short circuit.
Note:
Wires must be reconnected to the same side of the switch (i.e. top left / bottom left or top right / bottom right)