Re: Interior and exterior lighting

The tail and running lights are powered by the tow vehicle and the interior lights are powered by the RV, so power does not seem to be the issue. That leaves ground. But doesn’t seem to me like those things would be wired with a common ground. But with these things nothing surprises me.

First I would use a voltmeter to see if there is power at those light fixtures. If there is power, then ground is the most obvious problem. If no power to the fixtures, then it would seem you have two different issues as they use separate power sources.