What would cause tail light failure on a BMW Comp but all the lights seem to be working well?

This can be tricky. first make absolutley sure ALL lights are working correctly, back up lights, license plate lights, turn signals, third brake light and all exterior lights are working. and also make sure they are all the same light brightness. if all are good then i would suggest seeing what light it says is out in your instrument cluster,i assume its a rear light. go in the trunk and remove the tail light assemblies from the trunk, (these are the main brake light circuit board assemblies that hold the bulbs) then disconnect the connector to them and inspect the pins, make sure there are no burn marks and they are all good, both in the connector and the circuit board assembly. if still no luck, check the rubber boot that the trunk lid hinges are by that route the wires through, you can pull the boot out and inspect the wires inside making sure none are damaged from the hinge of the trunk being moved. hope this helps.