Update: I took the clock down and unplugged it, and the stereo and shoulder belts started working again. The headlamps still don't work and the radio restarts itself when I go over speed bumps, but those are problems for another day.

For anyone who somehow found this after having the same issue:
Unscrew the exterior screw, then use a thin tool to pry open the headlamp covers, and then stick another thin tool (or a fingernail if you have them) under the opening. They will bend a bit but that's fine. Firmly pull them straight down once you have a good grip. You can now access the last screws holding the overhead assembly in place. Undo those yada yada the assembly will fall down, the wires will catch it.
NOW: the wire connector is very hard to remove. You will need to pry it open decently far while also pushing it out firmly. Eventually, the clasp will catch on the sloped bit of plastic. You can now push the clasp with one hand while pulling on the connector with the other. You do not need to disconnect the headlamps. Test your radio, then fasten the assembly back into place. Wahoo!