I feel sympathetic about your problem with your Highlander. This problem is not very rare as you mentioned. At dealer fixing it will easily cost around a thousand dollars. They should replace the circuit board in the climate control unit. The buttons and turning knobs are soldered on the board. The board costs about $7-800. I doubt if you can find an after-market one at a lower cost.
If you are handy and know about soldering, you may fix it DIY. Or find a friend who is familiar with hands-on electronic work to do it for you.You do not need to buy any cable or wire. Take the climate control unit off the central panel. Open the cover and expose the circuit board. Please remember each step you do, since you will put it back together. The problem is with the middle turning knob (temperature control) wiring. You should see a ribbon cable with three wires from the circuit board to the knob, and one or even two wires broken off its/their soldering point(s). The cable should still long enough, so just solder the wire(s) back, and re-assemble the control unit. You should clearly distinguish which wire goes to where in case two wires need to be soldered back to where they should. Then re-connect the wire harnesses to the climate control unit and put it back in. Bingo. you save yourself a thousand bucks!
