Engine has stalled

Ok. That means we need to check it for the ground signal at the PCM.

Ok. Locate the orange and light blue wire on the datalink connector. It should be set to ground during start and run. Follow that orange and light blue wire to the PCM, Pin 22. With the key in start or run, that should also be set to ground. This is the ground signal that matches the positive signal through the ignition switch. If there is no continuity to ground at any of the light blue/orange wires, you either have a bad wire, or if it goes all the way to Pin 22, a bad PCM.

According to the schematic I have, yes, one wire. And I have no idea how or where they'd route it. Find the PCM to start. Or follow it from the relay. Or both.

Ok. Pins 86 and 30 are good, then. You should see Pin 85 going to ground for 2 seconds when you turn the key to on. If not, you'll have to undo the wrapping to see where it goes and what's wrong with it.
But test the output at the PCM first. Next, find and test it at the datalink. Locate the fault between the two components where signal is lost.

No. Pin 85 goes to ground when the key is turned on. For two seconds, unless the engine starts, then it stays grounded. You need a continuity tester. Hook the alligator to ground, and probe Pin 85 when the key is turned on. Then do the datalink. Then do Pin 22 of the PCM. If Pin 22 doesn't show continuity to ground for 2 seconds, the PCM is at fault. If it does, the wiring is. And you'll have to trace it.

Ok. We'll be here.

The PCM is located at the left rear of the engine bay. See image attached.

Look for the orange and blue wire and see if there is continuity between it and ground for 2 seconds after the key is turned on. If yes, locate the same wire on the datalink and check it. If no, it sounds like a bad PCM.