One problem related to headlight switch has been reported for the 2015 Tesla Model S. The most recently reported issues are listed below.
Tesla media control unit ("mcu") is no longer operable (screen turns black and loses all functions). The Tesla mcu is basically the car's central control system that allows you to adjust the headlights, the steering wheel resistance, the vehicle charging controls, the vehicle suspensions. . . Etc. The screen turned black, my turn lights are disabled (as shown in image, lights will no longer blink), my headlights are disabled, my airbag functions can no longer be switched to off when needed, the moon roof cannot be opened, the ac system along with defrost/cooling functions are all disabled and inaccessible. The vehicle dashboard displays "please wait while vehicle system powers up" for anywhere between 1 minutes to 4. 5 minutes. The vehicle is not operable during the system power up when I enter the car. This issue appears to be connected with the mcu failure and have persisted and worsened in the months leading up to the complete failure on 7/16. I would have to sit in vehicle for 1-4 minutes, unable to drive the car because it is loading up. This shows that the mcu is extremely essential to the vehicle, and not merely a media unit as they have tried to convince with the name. It appears that the mcu fails after a number of years/usage due to the old chip that rewrites over repeatedly. The mcu is pre-installed to fail in all vehicles produced prior to 2018 in the model x and s. Basically this system will fail in every car at uses the old mcu1, and doesn't apply to vehicles after 2018 since the switch to mcu2. I reached out to Tesla service center by phone (unable to access the Tesla app due to the inability for app and vehicle to communicate), and they quoted a replacement of the same mcu (but with an upgraded chip) at the price of $1201, with a 3 week waiting period. The car is not inoperable for the next 3 weeks due to the lost of essential and safety functions.