2001 Volkswagen Beetle rear lights

Electrical problem
2001 Volkswagen Beetle 4 cyl Two Wheel Drive Automatic 100k miles

My rear lights are coming on all by themselves at night. When I come home at night and park the car, all the lights are off as they should be. Sometime over night, the rear lights come on all by themselves and drain the battery(only the rear lights). Could the brake switch be defective or is this an electrical problem? Has anyone experienced this? Any help would be appreciated. Thank you