I'm documenting the install of the Curt model 12100 hitch and 56040 wiring. On my 2009 Forester, I went with the Subaru OEM hitch. Unhappy with how that hitch replaces the bumper beam, and thus reduces rear crash performance, I went with the Curt hitch for my 2015 Forester.
The Curt hitch calls for drilling holes and slots in order to install. I achieved this without drilling by removing the rear bumper cover. All together, it took about two hours to install.
First, I used almost a full can of 3M 03584 rubberized undercoating to cover the hitch three days prior to install. It seems that aftermarket hitches rust easily, and this should give the hitch much better protection. It dried to a hard, matte finish.
Remove the two rear taillights - 10mm socket, and unplug the wiring connector.
Remove the rear splash guards, two screws and a plastic push plug each.
Remove the plastic push plugs from the bottom of the bumper. These pry out easy using a flat screwdriver blade.
Remove the push plug at the top edge of the bumper cover - in the wheel well. This was a little tricky, as you need to pull back the plastic wheel well liner a bit, and using a flat screwdriver, push the retaining pin out from the plug.
Pull the bumper cover out from the side - snaps out, and then the whole cover comes off fairly easily.
With a deep well 14mm socket and extension, remove the 4 bolts and 2 nuts holding the bumper beam on. Take the beam off, and then from inside the frame rail, push out the 3 plastic plugs. This is where the bolts holding the hitch will go.
With 14mm socket and wrench on backside, remove two bolts connecting the muffler to the pipe.
Remove muffler, then remove the four bolts holding the heat shield. I squirted a bit of wd40 in the rubber hangers to get them to slide out easier.
Prior to taking the heat shield down, hold up the hitch in place, so you can estimate where to trim the shield to access the bolt holes. Trim the shield with tin snips, then reinstall three of the four screws. There is one screw you won't reinstall, as it is in the way of the hitch.
From inside the frame rail, install three of the bolt/rectangular washers into the holes. Repeat for the other side. With a helper, put the hitch in place, and tighten the nuts to the prescribed torque.
Reinstall everything you removed in reverse order.
The wiring is very easy to install. Remove the spare tire, remove the plug at the bottom of the tire well, and cut a slit in the middle of it. This is where the wire will go thru.
Pull back the trim panel on the drivers side, and you will see the connector (wrapped in blue tape). Remove the tape, and install the plug from the 56040 kit. Apply the double side tape to the module, and adhere to the floor of the car well behind the trim piece. Push the wire thru the rubber plug and reinstall. Attach ground wire to bracket near the connector.