2000 XJ.. front drivers side, hangig inside from the caliper and behind the axle housing... looks like maybe a vacuum line? Can't for the life of me find where it goes.

 

front diff vent?

 

Nope.. come from up above somewhere

 

Looks very much like a front diff vent tube. For the sake of crossing it off the list, is there a vent tube connected to your diff currently? The other end attaches to the side of the air box or fender with some clips. Perhaps that is the other end of it, in which case it's meant to sit as high as can to prevent water getting in.

 

I'm having a hard time wondering why you haven't pulled on it and stuck your head under the hood looking.

My guess is breather hose too. Is yours attached?

 

Maybe it came loose from the diff end?

 

that is most definately a vent hose. either front diff or transfer case, most likely front diff because the t-case vent hose wouldn't be long enough from the factory to end up there

 

Front diff vent would make sense... I got a look at it and it goes up and sits against the firewall on the driver's side

 

Back of front diff on top

 

Correct!

Yes! It runs from the front diff along the fire wall. It must have fallen.