I was wrong, the photo is the in-car temperature sensor that is on top of the dash...in the middle. It appears to have separated from the grill piece that's visible from the top of the dash. It's been 10 years since I've changed mine on my 560SL, but I believe you can access it easily by removing the glove box. If you end up doing this, it's a good time to change the hose that sensor connects to, as they deteriorate with age. If the hose is broken or leaks, there won't be any air drawn by the sensor and your desired temperature won't be obtained. Good luck!!

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All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL