Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove both the 4 way plug from the PCB and the plug from the gas valve.
Measurement:
Test 1:
Measure the resistance of the red and black wires to check their continuity.
Expect zero resistance or continuity on each of the wires.
Test 2:
Measure the resistance between the black wire to earth and then the red wire to earth.
Expect open circuit for each of the tests.
Inspect harness and plugs for good overall condition.
Measure the resistance of the red and black wires to check their continuity.
Expect zero resistance or continuity on each of the wires.
Test 2:
Measure the resistance between the black wire to earth and then the red wire to earth.
Expect open circuit for each of the tests.
Inspect harness and plugs for good overall condition.
Isolate as per TOPs P4
and refit as necessary