I'll be adding a hitch and wiring soon. I've done this operation before on other cars, by running a fused wire from the battery or junction block, to the converter box located inside the rear of the vehicle.

 

My application will not use brakes, trailer GVW is about 900#.

 

My question is: the Outback has a place in the fuse box for trailer supply. Is there also a wire running to the rear, or do I have to run one?

 

Naturally, if in doubt, I'll just run a #18 wire with heavy insulation...

I would kind of guess there should be a wire back there, but I can't confirm that.

 

You may want to also ask over here if no one has an answer for you.

http://www.subaruoutback.org/forums/

I've had 3 different OBW's, all different years, put a trailer hitch on everyone of them, and the required trailer light connector was always there hiding under one of the back cargo side covers, on one side or the other. My present ride (07) hid it on the driver's side. I always purchased the factory hitch and the trailer wiring harness came with it and plugged right in. I suspect that your 2010 will do the same. Good Luck!