One owner car, so history is known

Found two typos. I can't seem where to correct.

1) 145,000 miles total

2) can't help but THINK of a poor connection. (Not "thing")

Thanks to any who can help me solve. Trying to fix this one for my parents with minimal budget available.

I've been through most of that list already. I checked for spark a while back and that was okay. Hard to recheck at the moment with no spare set of hands. Fuses all appear fine, though nowhere do I see the fuel pump listed on a fuse, so I wonder if there is an additional panel. The one I'm finding is above the driver's left knee. It has 20-some fuses and a pair of breakers. Breakers are marked for windows and something else-- nothing to do with fuel, so I haven't tested them.

Either my memory was faulty or the gas gauge behavior has changed as it now sits above full (which I'm confident is not) with the ignition on or off. Also, It may be noteworthy that the real trunk closer no longer draws the trunk down tight, nor does the trunk release seem to work in the glove box (with the ignition turned on either).

The car is awkwardly close to a wall on the drivers side and cannot reasonably be moved. I read somewhere of a ground buss near the door jamb under the carpet on some similar cars. There is a big hump between the driver's seat and the doorjamb. Pulling the rocker cover strip and lifting the carpet, I see a large bundle of wires that looks like it was never touched since new. I can't see any sort of ground buss under there, but I have to wonder if there is something like that in play here. There is a bit of rust he and there around the car, though this is a car that spent life since new in Georgia so were not dealing with salt-related grade rust. Still, there's enough oxidation showing on mounts and brackets that I can see an open ground connection could be iffy somewhere.

Is there a common area for a ground buss to check which might involve the fuel pump, the fuel gauge, and the trunk release and auto-closer? My gut says to look for oxidized, poorly connected grounds, but I'd like to know where to look before I start tearing the car apart. Is the a buss hiding under the drivers seat? Should I pull that and check there first?

This is a nice old car, but really I just want to get it running safely and sell it for my mom. I'm not looking for some involved restoration project.