Fixed that electrical issue. As is so often the case with DIY, ‘twas partially my own damn fault. Fortunately it was easy enough to test and fix with my trusty-dusty multimeter. A wire had gotten corroded and when I replaced the switch that had become the issue, I didn’t hook it up properly. It was the corroding part that caused the circuit-outage issue, and I replaced the switch while troubleshooting (since it was obviously bad).
Not sure what corroded it in the first place, though. Little worried about that.