Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect connector X1 from the pump PCB

Measurement:

Check for continuity (zero resistance) of the two wires running between the main PCB (pins 3 and 4 of X3) and the pump PCB.
Inspect the harness and connectors for good overall condition.