Diagram for 87 yj vacuum lines for 4 wheel

SOURCE: 4 wheel drive problem on Jeep YJ

you can also check the 4 wheel drive vacuum switch on top of the transfer case...got mine for 10 bucks from parts store...fixed the problem

SOURCE: VACUUM HOSE DIAGRAM FOR 1988 JEEP WRANGLER 4.2 I6?

here is a link with all the vacum diagrams for your jeep. hope it helps.
http://www.autozone.com/addVehicleId,1076002/initialAction,repairGuide/shopping/repairGuide.htm?pageId=0900c1528008ab9d

SOURCE: 87 chevy s10 4x4 vacuum diagram

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Vacuum and Vapor Hose Diagrams Notes Vacuum Actuation System

SOURCE: need vacuum diagram for 4-wheel drive

the 4x4 don't use vacuum. the front is auto lock when the transfer is engauged with the button. if the light don't which when pressed into 4hi or 4low. the motor on the transfer case maybe hung up. they have to be used at least 4 times a year not to go bad. the motor is on the back side of the transfer case. best of luck.

SOURCE: 87 jeep wrangler 4 wheel drive don't engage

remove the vacuum hose from the shift motor on the front axle.with the vehicle running,(be sure to set parking break and /or chock tires.) place your finger over the end of the hose check for vacuum,it will be very slight. if there is no suction it is probably the vacuum switch on the transfer case. if there is vacuum,first check the vacuum motor for holes.(they rust through sometimes.) if no holes are noticed, remove the shift motor and check the shift fork. if the 4wd indicator light comes on it is probably the shift fork.