Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect connector X12 from the PCB

Measurement:

Measure for continuity (zero resistance) between the ends of the blue and black wires, in turn, from the disconnected X12 connector to the blue and black wires at the main terminal block.
Inspect the harness and connectors for good overall condition.