Newmar was doing something that some call cheap and others call smart.
If you are talking about a 3 way switch then look for this.
What Newmar did was to have 12 volts go to one side of the switch and 6 volts to the other. So in the up position the lights are bright because of the 12 volts and in the down position they are dim because of only getting 6 volts. I know this because that is how my 06 MA is wired.
So check your battery bank and look to see it there is a wire hooked to one side of a battery (12-14 gauge) then follow the wire to the in line fuse and see if its OK. If it is then good luck finding the problem.
2006 Mountain Aire, Jeep LJ, 900 watts of solar, boondocking life away! Volunteer Fire Fighter!