I have bought tablet type monitors for the rear headrests they are not direct plug in they have brackets for the headrests, they have no battery to charge and as such require direct wiring into the head unit to work, the cables have a thin red 12v cable for live a black for earth and three audio cables, so does anybody know if the S class has a facility somewhere for the the connection and how easy is it to install, is it a workshop job at Merc?