I finally got the brake system warning light in my beetle back to something like working condition. In the photo below, I have turned the key to "on", so the two red warning lights at the bottom of the speedometer are on (left side of the photo). What's new is that the brake system warning light, which tells you if you have lost the fluid in one of the brake circuits, is now working and thus is lit up to test with the other lamps. It's in the upper right part of the photo, just to the left of the headlight switch.
A major amount of work to score a minor victory--but as a result there are several more electrical circuits on the car that I've crawled through.