Hi ! Welcome to IRV2! We're sure glad you joined us!
Do you have a voltmeter? Check for 12VDC at the lights. Do these lights normally come on with other lights? If so, it could be a bad connection at the last light in the string that is working, or at the light that isn't working. It could also be a 12VDC fuse blown.
Good luck, happy trails, and God bless!
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Joe & Annette
Sometimes I sits and thinks, sometimes I just sits.....
2002 Monaco Windsor 40PBT, 2013 Honda CRV AWD