Alternator?

[Batcave]

While I was replacing the plugs and air filter this weekend, I found a dangling wire under the car. I found where the plug belongs and was able to plug it back in. It's beside the alternator, but I'm not sure it belongs to it.

The car ran fine without it plugged in and was wondering if anyone can identify what it is?

It's a 2001 C5 A6 2.8.

Thanks!

The photo is from underneath and the bottom of the photo is towards the rear.

[Brandywine050]

Air injection pump? i recall allroads had them mounted on the intake and the a6's were mounted near the passenger side frame. some one may need to chime in on this one though.

[Batcave]

Air injection pump? i recall allroads had them mounted on the intake and the a6's were mounted near the passenger side frame. some one may need to chime in on this one though.

Thanks! I think you're correct! I found the part online as well as a Youtube video and it seems to be that!