I'm guessing the display light saying the brakes are out?

If you aren't already aware the E53 has a common problem across all years with the tail light circuit boards creating too much heat and losing contact intermittently.

Do a search you'll find tons of threads on the issue, you'll either need to repair the circuit board by adding more solder and some epoxy to the plastic support, or hardwiring the sockets using a MB part to fix it on each side.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards