I am attempting to address my lack of 4 wheel drive in my truck again. It is a '97 F150 4x4. The 4 wheel drive is not working. Upon opening the hood and looking behind the battery, I noticed two things: A blue and a red hard plastice tubing that went absolutely nowhere. There was a slight suction on the red tube. I think these are the tubes I found melted underneath about a year ago and just hid up there after not being able to determine what they were for. There is also a small circular plastic piece that looks like a diaghram. There is a vacuum leak underneath that one. Not sure of there was some type of nipple on there that possibly broke off. I have pics of these but I guess I am not allowed to post attachments. Can someone shed some light on this situation for me. Thanks in advance

 

These tubes are the vacuum lines used to control the vacuum motor attached to the front differential. This activated the CAD, Central Axle Disconnect. There is a black cover on the passenger side of the front differential that has to be removed to access the motor. The other end of the tubes go to the solenoids on the firewall. Looking towards the firewall behind the battery you should see them. Closest to the fender is the engage line, red, and closest to the engine is the disengage line, blue. The picture below should help.

JMC