Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the 12 way connector from the front of the PCB
Disconnect the diverter valve plug at the inline connector

Measurement:

Measure the resistance between the red, grey and purple wires
from one end of the disconnected connector to the other in turn.
Red to red
Purple to purple
Grey to grey
Expect continuity on each test.
Also inspect the condition of the harness, visually checking
for any damaged insulation.