Really, it can go either way. If you want to keep things simple, it can be just as easy as tapping the switch wire and laying the sill on top of the door.
My install, however, took about two days of work...but I think it was worth it. No splicing, no cutting, kept my original sill (important to me, cause it would cost $300+ to get the same sills from the dealership if I ever wanted to go back), system is fully removable without a trace, and no exposed EL strip or wire.
The only complaint I have is about the build quality of the sill itself. It doesn't sit perfectly on top of the MB sill, and has a slight overhang on the inner and outer edges. I still really don't see why someone doesn't just make a full replacement sill instead of a stick-on-top one.
Of course this is on a 208....so maybe the 202 one you have may come out better.