Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the black wires from the overheat thermostat

Measurement:

Measure the resistance between one of overheat thermostat terminals and the screw securing it (it does not matter which terminal or screw).
Expect open circuit (O.L).
Is the resistance measured as expected?