Defective Lamp

The "Defective Lamp" warning on my 98 E300 Turbo Diesel stays on even though I have replaced the lamp. I checked all the other lamps, including license plate lamp and can find no other bulbs with problems. I insured that I used the correct wattage so that is not the problem. There is a double rectangle indicator showing up on the dash next to the "tripometer", is this telling me something about my lamp problem. I do not remember seeing it there before. Does the dealer have the ability to pinpoint the defective lamp or are they going to just start replacing bulbs like I will do next. Any help appreciated.