Here is a link for the power connectors on a RV:RV Wiring
Pin 4 is 12V from your tow vehicle, check this voltage with the truck running. If you don't have 12V here there is a problem in the truck, maybe you have to install a fuse in your truck. I had to do this on mine. Your tow vehicle will not charge your battery as fast as the converter can.
You did not tell what tow vehicke you are using, this may help if we know.