Vacuum help..
 

1987 Jeep Chereokee XJ 4.0

OK. directly under the radiator bottle on passenger side firewall there are four colored lines red, yellow, blue, white, green. The blue one has a top looking thing that is black and big around as quarter where the blue line goes into it. but coming out the opposite side of black thing it plugs nowhere. Is this what may be keeping my 4 hi light on? If not what is it for?

This is the vac line for the 4wd with the 2 piece front dana 30 axle... I can't remember specifics since I don't have the 2 piece axle on my 87.. Check these lines extensively, I know that vac leaks are the primary reason for most 4wd failures/disengagements or failure to engage in these type axles. Good Luck...