97 2door XJ

I have a wiring problem with my 97 XJ. I have erratic gage function, no odometer, and other lighting problems. I purchased the Jeep with the gages not working and am trying to fix all of the problems you get with a used XJ that has been "tinkered with". I have tested and found a short in the system that appears to be in the front wiring harness of the PCM. When I disconect the harness there is no short to ground at the battery. It does not solve the problem, just the short to ground reading. I am trying to find out a way to test to see if it is the PCM or in the wiring leading up to it. I was also told it could be the BCM or body control module and should find out before swithing out the PCM. Any ideas on how to test this or diagnose this problem further would be extremely helpful. I am by far not a wiring expert and this has been extremely frustrating!!