As per OEM specs, the seat heater elements are actually stitched right under the leather and above the foam padding so that you can feel the heat more. If you were to retrofit elements, these would have to be installed under the foam pad so the heat transfer would be a bit less effective. Original parts would include the switches, wiring and perhaps a control module. w211 cars went to a separate control module in 06 so the CLS may have this as well. The control module times the heater on time.