You're probably (1) not on shore power, (2) the battery is switched Off, or (3) you have blown fuses typically caused by connecting the trailer battery backwards -- much too common mistake with dozens of threads
. Solar power doesn't power anything and is there to charge the battery. And, of course, it doesn't do a thing once it gets dark.
As noted the interior lights are 12vDC. If connected to shore power they will run off the 12vDC from the converter, if not they'll simply run off the 12vDC battery assuming the battery is switched On (and the battery is connected properly).