Hiya,
I've had a look at the wiring diagram and it shows that the lights are solely controlled by the switch on the facia panel of the appliance.
Only the fans are controlled by the microswitch on the hood.
To cure the problem you would have to replace the switch, part number 165316.
Click here for the switch
Hope this helps
Let me know how it goes.
Thanks
Home Appliance Technician
Whitegoods engineer working for a multibranded national company in the UK.