Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Gain access to PCB (use Insulation Mat as required)
Disconnect M5 from the PCB
Disconnect blue wire from the APS

Measurement:

Measure the resistance between pin 31 (Blue) of the disconnected M5 plug to the disconnected blue wire at the APS.
Resistance should be short circuit (zero resistance).
Inspect harness and connectors for good overall condition.