2008 subaru outback

Return the vehicle to the Uhaul dealer and demand that they repair it. It is evident, by your description, that they bungled the job. If they refuse, contact the Better Bussiness Bureau in your area and have them contact Uhaul. Most Uhaul dealers do excellent work and they have a great reputation....so try and work with the rep and they will most likely fix it for you for free this time, since they didn't get it right the first time. Best Wishes

Is there a trailer hitch wiring that could be causing your problem??

Sometime around 2000, GM started putting trailering pre-wire harnesses in the vehicle. Your truck may have this harness built in and would greatly simplify brake controller installation. Look under the glovebox and see if there is a wire harness tied off. There will be four wires in this harness, which should be run over to the steering column to use it. Most trailer brake controllers are compatible with this harness.
The four wires in the harness are: Red, 12vdc; black, ground; blue or purple, brake pedal; and brown or white, trailer brake wire to seven pin, four pin, or five pin connector at trailer hitch, if your truck came from the factory with a trailer hitch.
If you are adding the hitch and do not have the four wire harness, the under hood wires from your brake controller are Red, connect to one of the studs under the distribution box cover (the distribution box is on the driver's side against the firewall. Underneath the cover are two large threaded studs which are hot from the battery all the time); and the other wire from your brake controller would have to be run the length of the truck along the frame, tied off in several places, to the trailer hitch connector on the bumper. Follow the directions that came with trailer hitch wiring connector to connect this wire to the proper pin in the connector.
If this has helped you, great, and please remember to vote/comment.
Good luck!

is there a trailer hitch on the car if yes unplug convertor box, also look into tailgate harness were it passes into body could have some broken wires in this pass thru

that's because its to plug in for an electronic trailer brake controller

Did you change the plug under the dash on the passenger side?