Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X13 from the pcb
Remove the connector from the diverter valve head

Measurement:

Measure the continuity of each of the wires in the harness.
Red to Red(R)
Black to Black(B)
White to White(W)
Expect zero resistance or continuity.