SUCCESS! FINALLY!
I worked for 45 minutes trying to get that nut on the top wire, and decided I'd have to take the starter back out to do it, only to find I'd done too good of a job tightening the top bolt and couldn't loosen it. Came in for lunch, skimmed some videos hoping for a view of the top cable end to be sure I had it on correctly. One video of a '98 Explorer had a view of the starter through the wheelwell. I already had the front tire off just to get it out of the way, and knew you can't see the starter through the wheelwell on a Sport Trac. There's a heat shield in the way. Turns out the shield is easy to remove - 2 8mm screws into the top of the frame and 1 8mm bolt inside the frame. Not much clearance for the top rear screw, and limited clearance on the one under the truck, but a Gearwrench worked well. Once it's unbolted, the shield can easily be moved out of the way and you can see the connections on the solenoid - probably the top bolt, too. If your arms are long enough and you don't have too many layers on, you can reach up under the truck to get, and hold, a socket on the fasteners with your left hand and reach around through the wheelwell with your right to turn the ratchet! The shield is one of the obstacles that limit how far you can turn the ratchet, so getting it out of the way gives you more room for that, too. That was one of the few things that went without being a total pain that took 10 times longer than it should.
Once I reconnected the battery, the engine turned over noticeably faster than it has been - this with the old battery. I tested the new battery with my load tester as I thought it might be a dud based on the readings from my digital volt meter. It checked out, so my meter can't be trusted.
I started the engine, shut it off, and restarted it right away. The I let it set for a few minutes, and restarted it. Drove it on an 11 mile loop to get it good and warm. All told, I started it 6 or 7 times in an hour and a half at varying intervals. My son drove it tonight without any problems, so I think I'm done with this truck for a while!
I'll probably post a recap of what I did and learned so people don't have to read through all of the above.
