e46 loose wire

Hi gents, I recently bought an e46 330d (2003) and I have noticed there is a loose wire hanging under the car on the right hand side near the right rear wheel. It looks like its in the same sleeve as the brake sensor but I'm not sure. Its a brown and black wire, here is a pic of it:

Image may be NSFW.
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Does anyone know what this possibly is? The brake light is on, but that might be due to the worn out pads and the PDC does not work, it gives that long beep when shifting to reverse.