may be the alternator...seems like anything electrical may be the alternator <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

but i'd be inclined first to follow-up on the first-hand experience expressed here and at that automotiveforums link above

and check out your brake light circuit; remove bulbs, check bulbs with ohm meter, check connectors, sockets,etc; possibly clean contacts and reinstall or replace bulbs.

good luck
i love a good intermittent electrical challenge. . .especially when it's someone elses <img src="/forums/images/graemlins/smile.gif" alt="" />