I don't have any answers - but pay attention to everything when you hook it back up, the previous owner may have intentionally disconnected them...
Many moons ago, my first car was a 1982 Volkswagen Rabbit. It had been around the block by the time I bought it (read: the back seat floor was rusted out and you could watch the highway go past!). Anyway, the horn didn't work. I took it to the local service center for something and they kindly reattached the horn for me - no charge even! It was great until I started down the road... THE HORN BLEW ON EVERY RIGHT TURN! I re-disconnected it.
Anyway, maybe the PO disconnected it because the brakes were malfunctioning in some way.