Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Unplug connector X15 from PCB

Measurement:

Test the resistances between the wires at the disconnected connector block.
The Readings should conform approx to the table below:
LeadsOhms
Grey & Yellow9.3 KOhms
Red & Grey 8.3 MOhms