Hi Oliver, well like most things electrical you need a DIAGRAM, it's not really possible to say exactly what you need to do unless you can either visualise the thing or follow the drawing, it's quite easy to show you how to wire up the brake light but near bloody impossible to tell you over the internet without spending 2 hours describing what you need to do which would really only be a vague description at best, get a manual off ebay or such and that way you will know what goes where, a few quid spent on the right book can save you hours of frustration and blown fuses. If you don't have the slightest clue how to do most of this then mate your in for a really frustrating time, it's not something that just happens you have to learn how first, sorry to be negative but just picking other peoples brains wont cut it.