If you use the 92-95 wiring, it's not hard. 96+ when they went OBD-2 is a rats nest, stay away from that one if you're not comfortable with wiring.

I grabbed a 95 harness from a jeep grand cherokee at the junkyard. Start at the engine computer and work your way out from there. The wires go directly from the engine computer to the sensors. Unbolt all your grounds. If memory serves, I disconnected the engine harness at the firewall. The only wires I cut during removal were for the oxygen sensor and speed sensor because the donor vehicle was on the ground with no tires and I couldn't get under it. I had to wire those up after the fact which sucked but at least it was only two sensors. Once you get the harness home you gut out the stuff for the donor vehicle's lighting, horn, starter circuit, windshield wipers, etc. Keep the alternator wires as the EFI computer has voltage regulator built in. You will find the engine control section is pretty self-contained making this part easy. I think the only connector in the whole thing is the one for the fuel injectors. After that it's just putting power, ground and keyed power to the harness to make it run. I installed some fuses too just in case. Also there's a switched ground wire that comes from the ECU to flash back engine codes so you'll want to wire that one up.

I used masking tape and a pen to label what sensor each connector is for. The charcoal cannister purge circuit I removed completely. I kept the cruise control wiring in place but haven't tried hooking it up yet.

To install, I installed my new engine and transmission. Hooked up by rad, exhaust and got all my mechanical work done. Then I took my old wiring harness, gutted out everything except the lighting, windshield wiper, starter and horn circuits and reinstalled it to make sure all that stuff still worked. Then I laid my (now gutted) EFI harness over top and ran the wiring to the sensors, figured out the wire routing and temporary taped the wiring all in place. Then I wired in my fuse holders, ran wires to my constant/keyed 12v sources. After I taped and zip tied everything into it's temporary spots I went to crank. Then key on/off/on/off/on to check codes with the flashing check engine light. Everything looked as expected so hit the key and see what happens. Mine would fire for a second, then die. Eventually I figured out the jeep ecu has security built in. I got an ECU from a Ram, problem solved. Hit the key and she fired right up and purred like a kitten. Then go back, do a final clean up, wrap all the wires together, mount ECU permanently, hang wiring harness on firewall clips, etc.