Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove gas valve connector from the PCB
Remove the electrical connector from the gas valve

Measurement:

Measure the resistance between each set of wires on
the gas valve harness.
Expect continuity / zero resistance on each test.
Also visually inspect the condition of the harness.