I disagree.
On a cold start with the sensor behind the radiator you get perfect readings immediately, which means your climate system knows what to do immediately. Very few people sit in an idling vehicle for an hour. So the sensor is accurate more of the time in this location. No affect from sunlight.
But with it moved to the mirror, now you get extremely erroneous readings as soon as you walk out to the truck regardless of how long it's been sitting. This throws off the climate control also, since it partially relies on that exterior reading to control ambient on the inside, along with the inside sensor behind the dash. In this case, the ONLY time the sensor is accurate is when driving at speed.
I would take a location in front of the radiator any day of the week.
Taken from an ASE study guide:
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