Got a new D-Sub connector to replace the suspect one, finally. Got two, actually, just in case, and indeed I broke one during installation. New one is on and seems to work.
Took the opportunity to cut some 1mm plastic for holding up the ribbon. Much better, but I'm only attaching it on the X-axis so far (which was the worst) since the other ones would require major disassembly.
Putting the D-Sub back on didn't make the hotend work. After some futile debugging of the connector (the firmware aborts when the thermistor is disconnected), I finally did the simple thing and measured across the male D-Sub and the wires. Voila, no connection on pins 3, 10, and 11. That would explain it.
Turns out one of the pins one the circuit board wasn't soldered well enough. Fixing that helped, now there's hole all the way through and it heats nicely, all the way to 230 degrees.
Calibrating the bed. Put in extra washers on the right side, which, once I re-read the instructions, turned out to be the wrong way to calibrate those. Front-back is fine, but the middle sags a little.
Re-adjusted the Z-height, but still want to do it like the instructions say. Not tonight, though. Also need to calibrate the extruder.