I bought one of those inexpensive thermometer gauges for the outside temp and removed the lower panel below the steering wheel posting the wire into the front door jam between the fender and the door. The degrees seem to be off by about 10-12 degrees so my guess is the heated air from the engine is causing this. My next try is going to be literally behind the side mirror, running the temp cord through the same path as the wires for the electric module on the arm rest of the door.

Anyone have any suggestions or bad experiences removing the side mirror? Does this sound like a bad idea? Thanks.

I ran mine from next to the instrument cluster, down to in front of the cigarette lighter, down the side of the kick panel, under the glove box, out the front seal on the passenger door, under the hood, along the top of the wheel well, above the headlight, down in front of the radiator and attached the sensor to the underside of the bumper. Works fine. I needed to solder on an extra 5 feet or so of wire.

There is usually a soft rubber bulkhead "grommet" on the Drivers side in front of the junction block where the wire harness passes, should be able to get "one more wire" through nestled up against the harness.
Like Brians idea of placement, where it counts.
There is so much turbulence around the windshield and cowl areas no telling where that air has been.

The area behind the mirror is not good there is a high vacuum there and will draw air from through the side window seals. I count on that when I am eating pistachios.

Thank you on the feedback. The placement of the sensor and the vaccuum warning- both good points and advice.

I couldn't find a bulkhead grommet in either my 4Runner or my Camry. They must be well hidden.