Check you voltage, check for water in and below blub in trunk. i read where car had this problem water in housing and got into lock pump and caused fire, i have seen some xfires on line where it appeared that fire started in taillight area area.i also found where a jumper harness having resistance that drops the volts by 1 2003 merecedes repaired this. also check the blub holder mined melted not getting go contact keep replacing blub replaced socket. also google about brake lights