This is probably your rear "fog" lamp. I do not know if it is an option on the E320 There is only one in the rear on selected models. To activate the rear fog lamp, with the headlamps or parking light on, pull the headlight switch out two clicks. (On my 93 300E, the first click turn on the front fog lights and the second click turned on the rear fog light -- when rear fog light is turn on, the center of the headlight switch lights up amber). Hope this apples to your model and hope it helps.