Polarity
I am giving some thought to the possibility that I simply reversed the wires on the battery connector for the Fuzz Face. While the wires on the other two pedals were red (positive) and black (negative), just like the battery connector, the wires on the Fuzz Face were black and white. I assumed that black was still negative and white was positive, but maybe not?
The problem now is, both my amp and my guitar have such finicky connectors that I was unable to get a note from the amp tonight, even without the Fuzz Face in the loop, so I haven’t been able to test. I’m tempted to use some 1/4” female to 1/8” male connectors (and a male-to-female adapter) to splice the pedal in between my MacBook and my computer speakers, because I know those work.
I’ve also started trying to map out the wiring schematic of the thing, just to figure out where to put the multi-meter to check connections.