Electrical Short - What Just Happened?!

Following up with some good news. I've been driving the car for the last week without any troubles, and wanted to give it some time before I reported back. Here's what I ended up testing & doing based on 67dart273's advice upthread:

Battery off: 12.X
Starter relay: 12.X
Starter: 12.X

Yet getting the car to crank was consistently the problem because I had no electric whatsoever. The only thing that would bring back the electrical was disconnecting the battery cables and reseating them. Every single time.

Using that as a clue, I inspected the cables more carefully. Both clamps were a little loose and had some play. I took them apart, sanded/brushed the wires, scraped away corrosion, and even sanded the ground to the engine block. I reassembled everything tightly, and it's started every single time since. On top of it, startup is almost effortless. In the past, if I had let the car sit for a few days, it would take a couple of cranks to get it going. Now, it fires right up.

I appreciate everyone's help. Sincerely.