My #2 fuse was burnt. Checking in the dark let you overlook things like that.

In my defense, it was a *very* tiny break, but a break nonetheless. I also discovered that the little cardboard card that shows what systems are on what fuse is intact in the cover. #2 does indeed fuse the horn, brake lights and reverse lights. Installing a new fuse fixed the problem.

I figure I shorted something when I was reinstalling tail reflectors, which are now *MUCH* brighter thanks to the chrome paint.

Thanks for the help!