(Meant to post this Tuesday, but I hit Preview and fell asleep. So here you go.)
Before I started anything, I took my multimeter and checked for the missing ground between pins 5 and 16. Should have gotten zero, instead got 11.4 volts. Did I check the right ground pin?
Appeased my sanity and cleaned the (mostly shiny) cables on the top side of the engine. Multimeter shows zero resistance between any two ends. (The starter terminals, the engine block ground, and the ground under the ICM will wait for when I'm not working 13 hour days.)
However, on the drive home, I decided to turn on all the accessories while idling at a red light; I watched my volt gauge slowly slide down toward the red zone. Those random puzzle pieces of my radio sometimes forgetting the presets and the occasional hard start now seem to fit somewhere. Voltage across the terminals is 12.6 when off, around 13.5 at warm idle. Time to claim the battery'* warranty?