The turn signal on your Mercedes-Benz is one way to communicate with the other cars while driving on the road. Traffic Law Headquarters reported that about 2 million crashes per year are a result of failure to signal.
A warning may or may not show on your Mercedes dashboard depending on its model and the problem. “Turn Signal Left / Right / Front / Rear / Side Malfunction” warning may appear on electronic instrument cluster on newer Mercedes models. Double check the turn signal light bulb of your Mercedes car. Make certain it is placed properly in the turn signal socket. Replace the signal light bulbs if there are corroded or burned. Check the correct wattage indicated in the owner’s manual and replace them with newer ones.
Find out the most common turn signal problems and how to identify it yourself.
Left or Right Mercedes turn signal NOT working.
Turn signal either on the left or right side of your Mercedes car is not working when pressing the switch or the turn light doesn't stay on. In most cases, a faulty turn signal switch causes turn signal problems. The turn signal switch and wiper switch are part of the combination switch which is found in the steering column behind the steering wheel. Replace the combination switch by removing the steering wheel; no programming is required. Take note to disconnect the negative battery terminal. The new turn signal switch should have the same part number with the existing switch. To identify the compatible part numbers, call your Mercedes Benz service Laguna Niguel dealer parts department and provide them the VIN of your Mercedes-Benz.
Front or Rear Mercedes Turn signal not working
A burned light bulb, bad SAM module, bad headlight, connector, taillight electrical plug or harness and burned turn signal contact may cause Mercedes turn signal not to work. What to do? Replace the signal light bulb with a new one that has the same wattage and bulb type. The electrical plug that plugs into taillight assembly may not make good contact or may be loose. Remove and inspect it. Use an electrical contact cleaner to clean it if needed.
Read more here: http://www.niguelauto.com/info-articles/mercedes-benz-turn-signal-light-issues-and-how-to-fix-them/