4x4 vacuum switch

4x4 vacuum switch on front axle

there are three line to diaprahm. 2 wheel drive the one in the center of the diaprahm as vacuum. when in 4x4 the yellow one as vacuum to it. the other seems to never have vacuum to it...tranfer case engages but no front axle lock up help....jim

so does that mean if the jeep is not running it can not be put in 4x4 because there is no vacuum ???????

The third line is a vent.

If you're getting good vacuum to both of the other lines then your problem has to lie in the actuator mechanism or inside the axle. Take the mechanism off the axle housing and be sure it's not gunked up inside. Also check for broken shift forks, engagement collar etc. If everything is fine there you probably have a hole or maybe even water or gear oil in your actuator preventing the vacuum from doing it's job.

Take that sucker off and check it out!