That's side/parking lights; they're not the same thing as DRLs. DRLs operate whenever the engine is running, they are brighter than side lights and have a much larger spread of light than ordinary dipped beams.
Not to worry...Anyway...I still haven't found working DRLs for Alterr's Citaro. You would normally control them from the light rotary switch, which is un-clickable in Alterr's version. Parking lights (Shift + L) are probably as close as you're going to get.