Which lights? Your interior lights? Your exterior Running lights? We are talking about an RV, Right?
Well, assuming that you're talking about an RV and a series of the interior lights that are wired to a single ON/OFF switch, I would check the following;
1- Your interior lights operate on your 12-VDC from your COACH battery.
2- The Coach battery is kept charged by your built-in Converter (Charger), which in turn is powered by your 110-VAC.
3- Use a multimeter and check the voltage across the battery terminals. The voltage should be; 1- approximately 14.5 VDC if it is being charged, approximately 13.5 VDC if the battery is fully charged, and 12.5 VDC if the battery is not charged.