Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove Change Over Valve Microswitch cover
Remove plug from base of Microswitch Housing
Remove Change Over Valve Microswitch cover
Remove plug from base of Microswitch Housing
Measurement:
HW Tap Off:
Resistance between black and orange wires is short circuit, black and blue wires open circuit.
HW Tap On:
Resistance between black and orange wires is open circuit, black and blue wires short circuit.
Note:
When continuity testing be aware that the colours of the wires change at the plug connection (microswitch housing).
Resistance between black and orange wires is short circuit, black and blue wires open circuit.
HW Tap On:
Resistance between black and orange wires is open circuit, black and blue wires short circuit.
Note:
When continuity testing be aware that the colours of the wires change at the plug connection (microswitch housing).
Isolate as per TOPs P4
and refit as necessary