No power to the starter

Thank you for the guidance. I checked the relay, and the starter does run when I place a jumper across terminals 3 and 5. I checked voltage between 1 and 2 and am only getting.9 volts when turning the key all the way. Should I be getting 12 volts there? I also checked voltage across 1 and 5 with the key on and got less than 1 volt. Based on that it appears that I am not getting voltage to the relay. I still do not get voltage to the OBD port. Lights do come on the dash, and I can hear the fuel pump running. When the starter was turning over with the jumper, the engine still would not start. Battery voltage was down to 12.2v after testing these things.
Do you have any guidance on the next steps? Thanks in advance.

Weather slowed me down a bit but thank you for sticking with me on this. My wiring connector to the PNP switch is a 9-pin connector as shown in the picture below. I am having a hard time finding a wiring diagram for this. I assume the two larger pins in the middle are what I need to jump but don't want to short anything else out.

Okay, I tested this, and I do not get any turning over when I jump 2 to 6.

I have a regular key (not push start) but it has a chip in it that is detected when it is in the ignition. Connecting terminals 4 and 5 did not cause the starter to turn over.

Testing across 1 and battery ground gives me just a tiny 2 mV. Testing across pin 2 and battery + gives me 12.1 volts.

Sorry for the slow follow-up. We had a few bad weather days then I was travelling.
I checked the voltage on connector D47 using my voltmeter from pin 2 (red wire) to ground. When the key was turned to start the voltage bounced around between 0 and 1 volt. When I released the key back to the start position the voltage went up to 10 volts. I double-checked the battery voltage, and it was at 12.2 volts.

It seems to me that we should be getting 12 volts when we turn the key to the start position. Earlier in this process, we bypassed the relay and ECM when we placed a jumper between pins 3 and 5 on the starter relay and we got the starter to turn over. That seems to indicate that turning the key to start is sending 12v out pin 8 on the ignition switch but not on pin 1 of the ignition switch.

Looking at the diagram power runs through that ALT fuse (120A) and the AM1 fuse (7.5A). The AM1 fuse was good but I am having a hard time figuring out the ALT fuse. It is part of a fusible link block assembly, and I haven't figured out how to get it out to know if it is good. There appear to be 5 fuses as part of the assembly but only 3 are labeled in the diagram on the cover. The pictures below are really hard to see but may help you see what I am looking at. The block assembly that is easy to see is a picture of the part taken off the internet for comparison. When looking at the picture the ALT fuse is located to the right of the picture. The picture of the fuse locations is rotated 180 degrees.

I double-checked. The starter turns over when I jump 3 and 5. The voltage on pin 1 has just under 1 volt when the engine is cranking but goes up to 8 volts when the key is in the on position.

So, I pulled wiring to the ignition switch and found that I wasn't getting voltage to the switch across pins 1 and 2 but was across 7 and 8. I traced back through the wiring diagram and after a battle getting the 120A ALT fusible link block assembly out, I found that it had blown, which explains why we weren't getting any voltage through. This was the fusible link I sent pictures of above but couldn't get a good look at it until I pulled apart the fuse box and extracted it. I have a new one ordered from the dealership. I am hoping I just accidentally shorted something when I reinstalled the alternator and that there isn't still a looming problem that will cause it to short again. I will update you when I get it installed. I really appreciate your time walking me through all of this. I have a much better feel for how to work through electrical issues now.

Okay. I was hopeful. I made progress but there is still something lurking. I replaced the fusible link block assembly, made sure all of my loose wires were connected again, tried to start it and got nothing. The dash and everything lit up, but the starter didn't even begin to turn over. I pulled the starter relay, jumped pins 3 and 5, turned the key and the car started up. I figured it must be a bad relay. Then I double-checked voltage across pin 2 and the battery + to make sure I had a good ground and got 12.6 volts as expected. When I tested the voltage across pin 1 and the battery ground and turned the key to "on", I got 8.5 volts. When I turn it to crank the engine, it drops to 1 volt. This tells me the circuit is not getting enough voltage to trigger the relay, so it is most likely not the relay.

Is it the computer? Is it a bad ground somewhere? Where else could we be losing voltage? I am also wondering why the 120 amp fusible link block assembly blew in the first place. This issue started after replacing the alternator and battery.

I will go back and check voltage into and out of the ignition switch and retrace my steps from before.

I went back through the circuit checking voltage and then realized that after I replaced the fusible link block assembly I did not go back and check the 7.5 amp fuse in that same circuit. When I originally checked it at the beginning of all of this it was good, but it looks like it probably blew at the same time as the fusible link. I dropped a new fuse in, and it fired right up and is back on the road.

Thank you again for walking me through this process. It has been a great learning experience.