[A/S] 7 way Plug

["trappersemail" <trappersemail@xxxxxxxxx>]

In the 7 way plug; where does the 12v+ go to on the tow vehicle.  
Seems as if I hook to the vehicle battery, every time I plug up all 
the batteries will equalize. . . that's a bad thing.  If I hook to 
the plus side of the alternator, same thing.  Hep mi ya'll.
                      TrapperJ