Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect plug from spark generator

Measurement:

Check for continuity (zero resistance) between the ends of the blue and brown leads that run from the plug for the spark generator to pins 25 and 26 at M4 on the PCB.
Check harness and connectors are in good overall condition.