Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the ST17 connector from the right hand
side of the PCB
Disconnect diverter valve connector

Measurement:

Check harness for continuity across all the wires at the PCB end to the diverter valve connecter.
Visually inspect the lead for good general condition.