You're lucky it hasn't gone 'bang' yet. If you keep swopping wires over for long enough, it will! Seriously, you need to understand what the wires are first. Unless your wiring is very old and dodgy, the reason why the light dimmed is because you've conncted it in series with the other lighting circuit. You need to look at a diagram of how lights are connected before you do it. Happy to answer any questions though.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!