Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect X5 from the PCB
Disconnect plug from diverter valve

Measurement:

Check for continuity (zero resistance) on each of the three wires running from the diverter valve to X5 at the PCB.
Inspect the harness and plugs for damage
and good overall condition.