Go to
http://colorado4wheel.com/manuals/Jeep/KJ/ for a copy of the FSM and parts fiche. I have no clue about an 03 but can say that there are mechanical and electronic cruise controls. Mechanical = a system that is physically connected to the throttle system and interfaced with speedometer/transmission/drive shaft which tells the physical connection how to manipulate the throttle to maintain speed. Electronic = the engine brain (ECU) is programmed to "have" a cruise function and directly manipulates fuel delivery to maintain speed. In both cases you need the system control switches. I'm pretty sure the 05/06 models have electronic systems and I know the controls and wiring can be added and the ECU programmed. Writeups are over on the CRD section of the forum.
FYI what difference there is between cruise on a manual vs. automatic transmission is beyond me. I do know both systems can have cruise.