I would go with it being a FR warranty item. Freightliner supplies the chassis, but the headlights are part of the body which is supplied by the coach builder. Somewhere in your owners paperwork you will have a Freightliner 1-800 number and have your VIN handy, they can answer any question you may have with the simple clicks of a keyboard. And I may add are excellent to deal with.
There is a good chance that they will say to bring your coach in to have it looked at to see if it is a wire harness issue.
But, I would at least give them a call for direction as to the proper route to go.
2013 Ford F350 FX4 4x4 PSD
2013 Wildcat 353LS
2015 Day/Nights Camped 5
2014 Day/Nights Camped 29