Guys,
I want to share with you my experience with tail lamp issues. It all started when some ignorant SOB hit my left rear in a parking garage. Broke the LR tail lamp lens boogered up the bumper. Well, I replaced the tail lamp lens, the bulbs and the bulb board. It all came as a single unit from Rock Auto. Genuine M-B parts for a fraction of the cost. A few months later, I received malfunction messages on the dash indicating the left rear tail lamp was on, the left rear back-up lamp was on, and the left rear brake light was on. None of them were. I pulled out the lamp plate and fired up my digital multi-meter. There was continuity to the bulbs and the plate. The ground wire to the SAM (signal acquisition and actuation module) had continuity and each wire had voltage. So, I decided to ignore it all and drive on. After another month, the messages changed from the tail lamps being on to all six lamps (license plate light, left rear) not working. Sure enough, the entire left rear assembly failed to operate. Broke out the DMM again and checked everything. All had power and continuity. Many of the online forums and chat rooms suggest everything from changing the bulbs to long life bulbs, replacing the plate with an MB original part, and replacing the SAM. I packed up my DMM and waived the white flag. The repair shop did the diagnostics and said the SAM had the power, it just wasn't sending the signal to the bulbs. So, $742 later, I have a new SAM with properly set parameterization, and working tail lamps. According to the repair shop, SAM failure is pretty common on older M-Bs. If you have this problem, I suggest you buy a decent DMM, and do some checks to see if you can cheaply replace a burned out bulb or broken plate yourself. Otherwise, it is big bucks on a new SAM. Oh, and by the way, you will still have to visit a repair shop or the dealer to have the parameterization set or the tail lamps still won't work. Isn't technology grand?