Added trailer wiring harness. Subaru and Curt make it easy - there is already a plug in the Subaru and Curt makes a harness that fits it. Most install instructions have you storing the the 4 pin connector in the spare tire well and just running it out the bottom of the hatch when needed. There were a couple of examples online, as well as on this forum courtesy of
@azxtrek that showed a nice bumper mounted plug and I used that.
This thread has video.
Curt wiring harness
Curt wiring adapter (bumper plug)
After removing trim pieces and spare tire, you'll find the plug here, for 2018 +. For earlier models it is tucked behind the trim piece in the corner.
On the passenger's side back of the cargo bay there is a port with a rubber plug in it. I had to widen it a little bit to fit the wiring harness plug through. Some people have trimmed the sides of the plug, but since it is going to be out in the weather I didn't want to do that.
I mounted the black box and tucked the wiring behind the trim piece in the corner. I did have to loosen the side trim piece to get enough room for my hands in there. Sorry for the blurry photo.
Here's the wiring routed to the port. Note there are two other ports in the bottom of the spare tire well that are larger, but if I used one of those I would have to route the wiring over the muffler and I was not sure if the wiring would stand up to the heat.
i drilled a 1.25" hole in the bumper cover to mount the adapter, and viola! I did clean up around the hole before sticking the adapter in.