Thanks again for the help by the way folks!

 

You’re welcome, you say you thought you checked a relay or fuse, double check it! And you say you have 12 volts, what does the battery have from positive to negative terminal, must be more than 12.5 volts.

 

The lead from the fuse box to the starter should be ALWAYS hot. The lead connected to the solenoid is only hot when the starter relay is activated.
The key causes the BCM to send a signal to the start relay which then sends a Positive signal to the starter solenoid which then activates the Bendix that throws the starter gear and engages the starter motor with a ground signal.
Understanding the start circuit might help in diagnosing, and the reason we ask these many silly questions. Since we don't know where or how this "arcing" occurred it is difficult to guess.

 

The arc may have killed the solenoid.

 

Update and conclusion for y’all Sorry I’ve been MIA since last week. My shop isn’t insulated, and with sub-zero real-feel temperatures most of the week, progress was extremely slow.



For the record, I had 12.7V across the battery terminals.



Since I was fairly confident I had already checked grounds, fuses, and relays both under the hood and inside the cabin, I went ahead and checked them all again anyway. All grounds were clean and secure. I didn’t find any blown fuses. All relays tested between 70–75 ohms, which to my understanding is within spec.



I rechecked power at the starter and had constant voltage at the feed from the fuse block, as well as proper signal voltage at the solenoid with the key in the crank position.



I’m not sure if this is a legitimate diagnostic technique, but I jumped the solenoid terminals with a screwdriver. The starter motor spun, but the engine did not turn over.



I replaced the starter, and Bobs yours uncle uncle car fired right up.

The only code I’m seeing now is for the MAF, and since it’s still unplugged, I’d say this one is officially resolved.

While I’m not the best at 12-volt troubleshooting, I’ll admit I got tunnel-visioned by the loss-of-communication codes from nearly every module and overlooked what turned out to be the simplest solution.



Once again, thank you both. You’re clearly the OGs on this forum, and who knows how many cars you’ve helped get back on the road over the years.

 

Glad you got it fixed and back on the road!