why is car smells burning plastic when u turn on the headlight

Hello, That smell is likely burning plastic. Have the vehicle inspected to find out the source of the smell, and the cause. This can lead to an engine or interior fire if not addressed. You may even be able to look at the fuse panel and see if it has melted. If you need a recommendation, check this list, and see if there is a BMW expert at any of these certified repair facilities: http://repairpal.com/bmw-within-10-miles-of-san-diego-california-92114