welcome to nico.
i had the same problem and its the tail light sensor box,its behind the driver side tail light
its a little green box.
what i did was i pulled the guts out (a circuit board) and there was a bad solder on one of the resistors(or capacitor)
i dabbed alittle solder on there and it works like a champ.
the box itself is like $70 iirc but i was poor and decided to look at it myself
hope this helps.
edit,here is a pic,its the green box on the right.(drivers side tail light)
