Mercedes don’t make it easy to “borrow” their cable runs that go from the van body into the doors. We wanted to put power cables through into the rear doors for powerful work lights. It was more effort than it should have been.
The trick is to first pull off the flexible rubber hose, then pop the plastic piece out using trim tools. It has clips at its corners. Once you’ve run the cable through (use a wire fish – there’s a tight grommet seal inside the rubber hose), re-attach the rubber hose to the plastic piece, then just snap it back in place.
It was worth it though. Now we have LED lights in the rear doors. They each switch on independently. They are really bright for working inside the van, but we designed them more for outside use. You can open the doors 90 degrees and have a well-lit work area at the back of the van. Or, you can open a door 270 degrees and light whatever is on that side of the van.