Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector from return thermistor

Measurement:

Check for continuity (zero resistance) of the red and black wires running from the disconnected plug to X7 on the PCB.
Red = Pin 5.
Black = Pin 6.
Inspect harness and connectors for good overall condition.
Note:
Wires may be multicoloured.