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How was the starter tested? Did you jump power to the S terminal on the solenoid? When you checked power to the smaller wire (s wire), you mentioned you checked it with the key in the run position. That wire only gets power in the start position. Is that how you tested it? If that is how it was tested, check the starter relay (see picture 1 below). Here is a link that shows how to test a relay:
What I would do is this. If the starter spins but doesn't engage, remove the starter and bench test it. See of the Bendix is kicking the gear on the starter outward. If it is, then inspect the flex plate for damage. Maybe there are teeth missing from it. Also, make sure it is properly seated.
I attached two pictures below. Check the fuses I circled as well. One last thought. If it won't engage with the key, see if it will in neutral. There could be an issue with the safety switch.
Do this and let me know what you find.
Images (Click to enlarge)
Sunday, September 1st, 2019 AT 8:52 PM