Ignition Fuse (15A) blows when key is turned on

[SixBucks]

2004 Ford Explorer XLT, 4.0L SOHC, 2WD, 150k miles
Drove it a few miles this morning, no issues. It sat for an hour or so, then would not start. Cranks fine, I have fuel. In the fuse/relay box near the battery in the engine compartment is a 15 amp fuse labeled Ignition Coil. It was blown. Put a new fuse in, blew it again. I had a known-good spare coil pack (long story), so I swapped them out. No change. As soon as the key is turned on, the fuse blows.
Any thoughts or suggestions?

 

[SixBucks]

Update: So, back in mid-May I installed a used PCM. Long story short, that is where my short was. I had my original PCM yet, which was functional. I had sent it to SIA Electronics to see if they could repair it. They said they played around with it, but determined the main chip was bad and therefore could not repair it. They shipped it back to me.
I tried installing it and when I turn the key on, the red light on the dash blinks fast and it will not even turn over.
Does PATS prevent the starter from engaging, or is something else going on too? Did SIA somehow wipe the program altogether?