Check rear lights warning on 2000 BMW 540i

I get a "check rear lights" message and my battery is being drained. I find no lamps that need to be replaced. Any ideas where to start looking?

Asked by for the 2000 BMW 540i
If this message comes on and all lights are ok, check the license plate illumination lights. If they are out replace whichever is out and also look at the trunk lid rubber conduit that all wires pass through. Wires there tend to "strecht and pull" everytime the trunk is open and close and will break. My drove me crazy until I noticed the plate light was out and looked into it.
2 more answers
Very likely the wires going through the trunk hinge, I had the same problem.
Don't forget to check the center brake light which sits in the rear dash. Access is through the roof of the trunk.