Door opeing activated lights

[iPhoneNerd]

Hi, I have a 2002 C180. I have installed some retrofit lighting in the foot wells, that give a nice modern looking glow to the foot well. They were just a cheep kit from Maplins and run via plugging into the cigarette lighter. Does anyone know how to connect them to the door switch?
At the moment the interior lights will illuminate when opening the door (as standard), I also want to connect these new lights to do the same.... Any ideas?