Can't help exactly ; but have to say the switch maybe a change over, for the microwave, water heater 120 volt power .
One of my first 5ers ( 30 amp power) you could use electric for hot water OR flip the switch to power the microwave .
The 30 amp system , would not handle , roof A/C , water heater and microwave at the same time , so you had to select WH or micro .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.