Check license plate lights too...you may have more than one bulb.

If this doesn't work, then try this:

Remove the covers off of both taillight housings and turn your lights on (engine running).

Are any of the bulbs (especially the night bulbs) on one of the housings dimmer than on the other?

A common problem is that over time, the metal strips that house the bulbs loosen from vibration and cause ground faults.

The cure is to press along the strips to reseat them firmly. You will see the results if pressing one of the strips changes the bulb illumination on either of the housings.

The "bulb out" indicator may or may not go out immediately...you may have to shut everything off and restart to see if the indicator stays off.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car