If you have access to a test light and/or digital volt meter and feel confident in using one, find the light switch and check the main feed to it for +12 Volts. If it's present then check the output to see if the +12V is getting through the switch.
It's just a matter of backtracking where the +12 Volts is being lost.
You say you checked the fuses, are you sure you checked all of them. Many coaches have fuses under the dash and also outside under the hood. Sometimes they can be double-fused.
Also, you should include your type of chassis and coach, model, make, year, etc. It could make it easier for those on this forum to help you more.
Bob 2006 Monaco Camelot 40PDQ
US Navy Carrier Battlegroup 1959/1963
Summer in Colorado, Winter Texas Gulf Coast