posi-lock ?

sorry newbie?
But I have been reading about this posi-lock cable for the front. But is that for certain years only? Something about a vacum line? Will it work on a 98? Then is this like an actual locker or does it do something else.

The Posi-Lock is a manual refit that replaces the vacuum axle disconnect on the D30 axles that had vacuum discos. After 91 or thereabouts, all XJs got the non-vacuum axles.

Your 98 came with a non-vacuum axle, so you'd have nowhere to put the Posi-Lock.

no onlu on jeeps that have the vaccum disconnect front axle.........you have no need for it