Scott, i like my lockers when a tire is OFF the ground...... flick the switch and jeep goes forward
instead of tire off the ground spinning. or does your YJ have so much flex you don't lift tires
pull the airline off the diff end. engage the locker. do you feel it pushing air? no? or yes?
no? check the line for holes. check the pump itself to see if its pushing air. no on both accounts maybe the pump?
yes you can feel it pushing air? reconnect it, make sure its not leaking at the housing.
after that i don't know; not sure how a rubi locker works compared to an ARB. do they have release solenoids? i'd check those too. (i have no clue on that, going on my ARBs)
check the easy stuff first that are not in the differential. i don't know if you have the same setup as an ARB where mine blows seals all the time. but thats a good place to start with the lines and pump. cheap and easy. if its in the locker itself not good!
hope you find it and its an easy fix. i'd be fumed off if i bought a jeep specifically for the lockers only to have them not work. otherwise i'd wheel a cherokee. a red cherokee. with a drop kit.... on 31s