I'm not sure. Although it makes perfect sense, I don't think anyone would use it like that. "Lysbryter" gives associations to a light switch found in rooms but I don't get the same feeling seeing one of these.
Not in general, no...but if you had to find a word to refer to the thing specifically? If somebody asked me "Hvor er lysbryteren?" in a car, I would probably point to the switch for the ceiling light, so it's not great, but it's the best I can come up with.
A "fjernlysbryter" is something else, so that's not it.
If you say just "bryter" then it does not necessarily mean "lysbryter", it can mean any switch. However, the Norwegians never use the light switch in their cars, as the lights switch on automatically after the engine is started. They just switch between the headlights in high (fjernlys) and low beam (nærlys) mode and the parking lights. So, yes, fjernlysbryter is what people usually use.