Weird fuse problem with 53 plate Zafira?

Hi,
I have recently bought a Zafira and I love the car, only problem is the horn wasn't working. After removing/inspecting and replacing every fuse in the fusebox I bought a Haynes manual and got a fuse diagram. The Horn fuse was missing, so I bought a fuse and popped it in - Hey Presto! My horn now works.
Since then the engine management light and the traction control light come on and stay on about a minute after after the car has been started.
Does anyone have a clue what has caused this? I'm wondering if something needs to be reset because of a memory loss from when I removed each fuse, or maybe the horn fuse was purposely removed by a previous owner/mechanic because of some shorting problem with the traction control?
Any help would be greatly appreciated