My CL stopped working and I needed a new module,
it is located in the right side well behind the speaker on my car. I found some working modules at a Pull a Part yard. I popped the cover off of mine and it actually was a small ground strap at the bottom left corner of the PC board that had come unsoldered. Take back the side mat, take out the speaker, there are a couple of little screws, loosen them a few turns but don't remove. Slide the module up about 1/4 inch and the module should unlatch and drop down to where you can remove it and unplug it. Best to disconnect the battery first and keep it vertical until you unplug it otherwise you will mess it up. I forget some of the details. Look at the ETM on e38.org/e28 as there is a wiring diagram and maybe an install picture.