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 the 4 pin connector at the programmer and X9 at the PCB

Measurement:

Check for continuity (zero resistance) on each of the 4 wires on the harness that runs between the PCB and the Programmer.
Check that the harness and the connectors are in good overall condition.