Headlight sensor
#2
MBWorld Fanatic!
If you are talking about the oncoming/exterior light sensor, I believe it is the unit behind the rearview mirror. You should be able to see it by looking at your windshield from the outside, it'll be somewhere in the middle.
Depending on the optional equipment, there can also be a radar sensor there, among others.
Depending on the optional equipment, there can also be a radar sensor there, among others.