Originally Posted by Brian B-P
Yes, and "a good place" would be out of the way of any knee airbags, which some vehicles have - I don't know about the Highlander. Even if you consider knee airbags unimportant, it would be wise to disable any knee airbag which might ram the controller into the driver on inflation.
Here are a couple of photos that show the placement of the Tekonsha P2 in our 2018 Highlander.
To make the photos easier to understand, I stuck some masking tape on the black plastic cable which brings the wires out from under the dash and on up to the controller.
The Highlander has a small rectangular pop-out in the under-dash tray. My cable goes through that. My only modification to the vehicle was to drill two tiny pilot holes for the screws that attach the Tekonsha's metal bracket to the tray. First you mount the bracket and then you attach the controller to it.
BTW, the rectangular outline on the left side of the photos is the hatch for the knee-level airbag. The installer had put the unit just to the right of it--not the worst possible location, but not good enough for me. The metal bracket was like a dagger pointed at my knee joint.