Hi All. Recently purchased 3 year old SLK250. Stunning motor with no issues.. except the interior light (and reading lights) do not work at all. Please forgive the question, but is the interior light an optional extra? I wouldn't have thought so, given the presence of all the switch gear. Fuses checked out ok. Don't think all bulbs would have failed at same time. Grateful for someone to enlighten me (no pun intended!).