confused

We purchased an 89 Jeep Cherokee Laredo for our son recently and have been replacing parts on it to get it running properly. It would run great but had some issues cranking. It would crank cold but not hot. Replaced cps, fuel pressure regulator, battery, alternator. Last weekend we replace the wiring harness with one off of another 89 Laredo because there were splices in the one we had. We also replaced the computer with the one from that Laredo and also the ignition coil. Then it wouldn't crank at all. It would turn over, but no crank. We switched out the computer and coil with the originals but it still will not crank. It will turn over, no crank. The engine is getting fuel, but no spark. We are completely baffled by this and were wondering if anyone had any ideas. Please HELP!!