I got home yesterday after travelling some distance for a vacation to notice a cable dragging on the ground. It is on the drivers side of the rear axle, about half way between the differential and the wheel. It comes out of the top of the axle. It appears to be some sort of vent I would think. Any ideas on what it is and where it connects to? It is definitely not a brake line.

 

Yep it's a vent. I can't remember the original location without going out to look at my truck but it doesn't really matter where you put it as long as it's up as high as possible and where water can't get into it!