So I told this little story to the dealership service department, and they were baffled. Never heard of anything like it in ten years, said they'd have to examine it very closely.
Here's what happened two months ago:
I drive a Subaru Legacy 97. I turned the car on and was about to shift out of Park to drive away, so I stepped on the brake and as I did so, my headlights dimmed, my radio volume shrank and all the interior displays hiccuped. I took my hand off the shift, all thoughts of driving forgotten, and started playing with the brake. It did the same thing repeatedly. After a few tries, I stomped on the brake and everything blinked off entirely for a second, and the engine nearly shut down.
The electricity came back in less than half a second -- it wasn't a prolonged outage -- just a brief interruption -- so the engine caught itself and stayed running. But for just a moment, the whole car had shut off.
This only happened once to that extent once, and I have been unable to reproduce it. Sometimes, however, braking does ever so slightly dim my interior displays, so there is a definite consistency to this.
Since the dealership had no idea, I thought I'd try tapping the infinite well of experience that is Mechanics.SE. Any thoughts?