Set Appliance State:

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

Measurement:

Check for continuity (zero resistance) between the connector for the code plug and:
The Black wire (marked 3.3) on X5.
The Green wire (marked 3.2) on X5.
The Blue wire (marked 3.1) on X5.
The Red wire (marked 3.4) on X6.