LibertyTC here has the 2004 KJ Service Manuals which he tried to send to me but I could not download them here on my side. All the other KJ Service manuals bar the 2004 and 2007 are available below but in the long run it would be ideal for you to have the 2004 Manuals for future use.
The 2003 manual will be close enough to the 2004 manual but the wire colors may be different....you can check the wire color going to the #4 injector and look for it going into the PCM.
If you pull the connector off injector #4 and disconnect the connectors on the PCM you should not get any reading from that wire to chassis using the Ohms setting on your meter while the battery is disconnected as there should be no splices coming off that wire.
If that wire is too difficult to trace because it goes deep into an inaccesable harness...you can cut the bad wire off at both ends and replace it with a new wire...taking the shortest route..and tape it up neatly. I have done this about 13 times on my 2002 Export CRD due to the wiring harness going through a metal channel under the radiator!
www.colorado4wheel.com/manuals/Jeep/KJ/
Section 8W has the wiring diagrams and the end of the Component Location section gives you the location of the splices/grounds/connectors with the connector pin-outs!
