It is as previously suggested the connection for a reversing camera, if you wish to fit a a camera if you remove your high level brake light and fish about a foot or so down you'll find the other end of the camera wiring. Depending on model, if you remove the courtesy light there may be more connectors up there too for a monitor?
Clever thinking by swift me thinks, also depending on your motorhome model you may find that it is pre-wired for a solar panel too, but don't ask me where the wiring for that is though I haven't found it mine yet.
Hope that helps.