The box-Pretty sure something previous owner added


The box 'looks' like it has a row of LEDS, the switch 'looks' like a momentary switch... which leads me to think (or just a WAG), a monitor that is briefly powered by pushing the switch. What it monitors or why unknown. Looking inside possibly see where the wires go might give a clue to its intended function.
The wires appear 14ga or larger so tend to lean toward power?
Though I would suspect that year camper it doesnt have a battery?
Being outside possibly connected inline on the umbilical cord to check truck battery? Again just guesses...