I finally had a chance to look closer at the old knock sensor harness, and found what I think was the problem. It's one of the of the few places I've seen on the X where they didn't make the wiring the exact length needed, the connector closest to the firewall has the same length of wire as the long one, it's just looped back and taped in. On mine the plastic wire protector melted over time since it sits directly on the block and once that melted, one of the wire coatings melted and it was shorting against the block. I probably could have just replaced the harness but that job takes so long to do I'm glad I just replaced the sensors too so I don't need to pull it apart again.
Next up I need to pull the rear wheels and adjust the parking brake, there's zero adjustment left in the cab and the handle doesn't hold the truck at all now. I'd think the cable snapped but there's a tiny bit of hold, just not enough to be functional.