Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove connector CN5 from PCB.
Removed wires from transformer connector block.

Measurement:

Measure the resistance of each of the wires in the harness running between CN5 and the transformer wires.
Expect continuity / zero resistance.
Also visually inspect the condition of the harness.