so I looked at the wiring diagram and compared the sedan to the wagon. You can see that the wagon has the extra connector and pin 6 and 3 are used for the power to the connector. If you look back down the line, they hit an intersection where the sedan and wagon wiring is the same. From there, they are both sharing the same fuse. (#16?)
I do believe that there is no supplemental 12v powering the rear trailer connector. It all comes from the same source(fuse).