I am looking to install an outside wall light, however to do this I need to wire it up to a power supply in my hallway preferably. Ideally I would like to replace an existing 2gang light switch (which controls the landing and hallway individually) with a 3gang switch, and incorporate the out side light to be controlled from this point also. However I am a novice at this sort of thing and have no clue if this is possible or how to do this, please could someone/anyone give me some advise?