My suggestion would be to find the 12V feed to the light circuit going into the slide and just reverse the - and + and that should solve the issue. On one rig we had, I had to do that because it was reversed in polarity in the slideout and the item I was installing would not function as wired.
On my present coach, some of the bedroom ceiling lights are of incorrect polarity and some LEDs will not work correctly.
Hope this may help. Happy trails bert
2006 Monaco Dynasty Diamond IV 42' Tag, ISL 400,(new to us), Residential Refrig, 10KW Onan, Bosch Washer/220V Dryer (previously 2003 American Tradition 40W) 2010 Chev Malibu LT