You can check the polarity of the cigarette lighter socket with a multi meter or, lacking that, you can pull out the charging station module by popping off the plastic cover plate and removing the screws.
The positive (red) wire should be going to the center terminal of both sockets.
Mine was wired wrong and not only did it burn up my iPod but it ruined the USB port also. The USB port reduces the current from 12v to 5v DC.
Forest River paid for a new iPod but still has not returned my call about the USB port.
The new one arrived from Griffin so everything is working now.
2015 Rockwood MiniLite 2109S
2012 Nissan Frontier V-6
Blue Ox SwayPro hitch