Is that under the truck, behind the front axle? Is your truck 4 wheel drive?

 

It's a vacuum line (red? Haven't seen that yet!). You can dig out the stub piece in the rubber boot, trim the other end and use rtv sealer to seek into the boot.

 

That is the the vacuum line that goes to your front axle disconnect.

 

Looks like the other one is broken or missing too.

 

Yup, you need both... one to engage the axle, one to disengage the axle.

 

I'm curious to see how your 4wheel operation is after you get this fixed. I discovered the same thing under my truck and wondering if I got crap sucked up in the lines. It doesn't seem like its totally engaging and has trouble disengaging too. It's probably something else and haven't really dug into the problem yet, but curious what your does.

 

Inspect the metal lines!!! They will rust up and block any vac going through them. I had this happen and they had the lines connected to them.

 

I was wondering if those lines were disconnected because the PO already put in a posi-lok system (hoping???).

 

Would be nice to know if his truck is 4x4, and if it actually works...... but, he hasn't been back since he posted.