Squeaking suggests metal-to-metal contact somewhere.
You could try process of elimination by hitting one component of the suspension/steering system with a quick blast of WD-40 a day. For instance, the first day try the front left forward leaf spring bushing, wait for the WD-40 to evaporate or wash it off, listen for a squeak, and move on to the next component/bushing/ball joint/etc, Until the issue is found.
Also, take a grease gun to all the zerk's on the front suspension. That might eliminate a few possibilities.
1989 YJ with '92 4.0L, '91 AX-15, NP231 w/ JB SYE, 5" lift, 33's, Warn M8000, Olympic bumpers