Yeah, just maybe:
That is--or WAS, rather--the location where the battery grounds to the chassis. A bolt went through that hole and through a captive nut on the other side of that panel. That bolt secured the chassis or frame ground from the battery's negative terminal and ensured that everything had a good ground return path to the battery.
The only problem is, THAT'S NOT A FUCKING GROUND ANY LONGER. What that is, is a nut and bolt stuck through a stupid-large hole in the panel, which may or may not actually make some limited electrical connection, but sure as hell doesn't make a good one.
I had to pull the inner fender liner to get a pair of vise grips on the no-longer-captive nut that bolt went through. Having removed the bolt, when I saw that, I thought, "Yeah, that's it, all right."
Had to drill an existing hole a bit bigger to accommodate the bolt; filed away paint to get a good connection, wire-wheeled the bolt, and buttoned it all back up.
Engine kind-of ran. It was missing, but at least it was idling without my foot on the gas. That's what I'd expect from a misfire on one or two cylinders, especially in anything bigger than a 4-cylinder engine.
Shut her off and then dove back in. Pulled the coil bar, intending to get a look at it, but I absolutely could not get the electrical connector to separate, so I decided to try something else first: spark plugs.
You may recall that some months ago (I don't even remember when it was, now) I bought a set of plugs for the old Jeepney intending to replace them; I never got around to it--but with the coil bar off now was a good time, and since I had the new plugs it was a trivial exercise to replace them and eliminate them as a factor.
Pulled the plugs, and YE CATS what a mess they were. Proper gap is 0.035 and these were more like 0.05 or even 0.06. Rounded electrodes, the whole bit.
...which makes sense, considering THEY HAD SEVENTY THOUSAND MILES ON THEM.
Got the new plugs, gapped them, lubed them with anti-seize, stuck 'em in, then replaced the coil bar. Said a quick prayer, then cranked her...and she started, and ran, smooth as you please. Gunned it a few times, and there was no hesitation at all.
Got out, walked to the front of her, and left a kiss on the top of the grille.
I left the Jeep running while I cleaned up my tools, since I couldn't go much farther today in any event; the sun's going down. And it didn't miss a beat, just kept on idling away, nice and smooth. Once everything was cleaned up I shut her down and closed up.
So I do believe I'll call that one "fixed".