I've only had my '01 X5 for about a month, and really have no idea of what's under the carpet. I know the radio is aftermarket, added by the previous owner, who bought it just to restore and swap for my old race car, but I haven't got ahold of him to ask about its' installation details.

So, referring to your photos, I saw the orange wire, and wondered if it is an original thing in an E53 (which I doubt, since the excess wire in the coil seems like something that a car manufacturer would eliminate), or is added-on. If aftermarket, then I most-likely wouldn't have the same on my X5.

You say it goes to the airbag module? Coincidentally, I have the right side airbag warning light on. But it was already on before I put the screw in. I presume I should eventually look under the carpet by unbolting the seat, slitting the carpet under it (carefully), and seeing if I pierced or severed another wire that may (or may not) be another mystery wire.