battery, converter issues

I believe that the converter is wired directly to the 12v battery(ies).  When you are connected to "shore power" and the positive and negative on the battery is connected that is when the converter will be working (and you should hear the fan).  The converter will be charging the battery, if it needs charging.  For the factory wired lighting in the trailer to work the battery has to be connected so that there is power to the trailer's lights, which are all 12v.  That is the same for the jack on the front of the trailer and the motor's for the slide out if the trailer is so equipped.  There are some other items in the trailer that require 12 voltage to work and require the battery to be connected.  Hope this helps.