this is a simple 15-20 min job with minimal tools needed , the list
1 medium flat head screwdriver
or pocket knife
1 T25 torx head driver/start driver
glass cleaner and paper towels
1 new 3rd brake light ( a given) w211 03-05 part number A211820 15 56
Just pop out the 9 black plasitc caps with the screwdriver and remove . then remove the cap in each side hinge ,it is easier if you pop off the small latch on the trunk hinge plasic covers as well. Take out the 6 star screws holding on the hard plastic trunk cover over the latch. the carpet piece
now just pulls down. you do need to pull it towards the front of the car due to the handles on the inside not really an issue it just slips down , then disconnect the button and then remove.the small light I just push it thru and then pulled it back thru carefully its more difficult to disconnect. Now the 3rd brake light has 2 plastic tabs the stick out
. you need to push these to the outward you can see how they hold on then carefully remove the back black LED part . you will need to wiggle it and then slide it to the Left side and drop out the Right end first. Then disconnect on Left side. took about 15 mins-20 mins first time.
The part comes complete with new a Red light cover. It also seems to have a better looking gasket than the one that came on it. The hardest part is removing the old lens cover
. I used a screw driver and pressed in the soft metal tabs on the front side you can see, then just used my finger on the back side of the tab to let it slip outward working from one end to the next. keep you new lens oriented in the right direction when putting the new one one. You do not bend any tabs on the new one. make sure you clean the surface real well , so It can adhere and create a water tight seal. slip the plug in and then put the LED portion on sliding it in on the Left side fist. then flipping up over the grey tabs then make sure you pull the black tabs back to the center I pushed in on the light from the outside to help keep a tight fit. Works great. you can only check it if you turn the ignition on like your going to start the car.
Read more: http://mbworld.org/forums/w211-amg/403594-diy-3rd-brake-light-replacement.html#ixzz3F91af7XB