I have an 2011 3455sa. That switch operates 2 overhead lights (in our unit) that turn on when the screen door is opened. If the lights are turned off at the light they will not come on. If the switch is bad a new one can be found from trekwood rv.
Its a great feature IMHO. For dry camping I added an additional switch on the wall just behind the door switch, so I can turn the lights off in the daytime when they are not needed.
2018 Chevy 3500 LTZ Dually Diesel 4x4 CCLB
2011 Montana 3455 SA. 6 point level up. Disc brakes. Curt Q24 Hitch
Progressive EMS. Valterra tank valves. Sailun G637 tires. ARP fridge control. All led lighting. Mor Ryde IS