Rh428WF

I have been working on my daughters 1997 XJ sport. I am having some electrical issues that is kicking my ***! I have completely rewired the rear lift gate and everything is now working. There were a couple other wiring issues that I can not figure out. The reverse lights were not working. I replaced the module on the transmission and still no reverse lights. I had a problem with the A/C not working as the one line was broken. Line replaced and is holding a charge. No power to compressor. When I run a jumper it works fine same with the reverse lights. After buying a Chilton's manual for wiring diagrams and looking on line I am still stumped. I had a mechanic friend hooked up a code scanner and there is no connection once hooked up. Like the computer is not reading. The Jeep came with a second gauge cluster which my friend advised that the computer has to read through the cluster as well. We hooked up both clusters separately and still no signal. The Jeep does run just trying to fine tune everything and get all the bugs out. Any help would be great. I am starting to think the wiring harness was replaced with a different year as several sensors I replaced needed a different year as the connection was wrong. Any help would be great.