The 2003 KJ uses a PCI bus.
Later years used mainly CAN bus with some PCI bus and some SCSI.
There are Theory of Ops sections and the Wiring Diagrams are in section 8W
You can download the Service Manuals for most years except the 2004 from the link above in the Stickies which is the link here:
http://www.colorado4wheel.com/manuals/Jeep/KJ
For the 2.5/2.8 Export models definitely also download the section "2.5_2.8 export diesel" as it covers the actual engine used in the Export models.