I have seen a bad bulb cause wierd things to happen, believe it or not. Sometimes the filament ends up shorting to the outside, and makes wacky things happen. And even better, the culprit bulb will still light! Try buying a new bulb or two for your brake light, and swapping it out, then trying the brakes and see if that gets it.
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)