Where should you tap into the wiring in a 2005 Subaru Legacy GT Sedan to install a trailer hitch wiring harness?

I have a 2005 Subaru Legacy GT (Wagon) and haven't been able to find a hitch. Does anyone know how to solve this problem? If I am able to find a hitch, I would then try to get the Outback trailer hitch wiring harness from my Subaru dealer. I would expect the wiring in the two cars to be the same, but I suppose they could be different. I noticed the Legacy wagons don't have the rear 12 volt jack that the Outbacks have. This is something I'd like to add too for one of those electric coolers. That would be nifty I think. Thanks . . .