Hmmm, I found a load of stuff about this including wiring diagrams... hang on a sec... here's a wiring diagram for starters, assuming the lighting circuit similar/the same as the series vehicles (LR carried on using standard wiring colours for years):
Clearly you need to be able to read a circuit diagram, if you can't then , as above, leave it well alone!
Looks to me it's like this :
Plain red is front side lights
Red w/Black is tail and number plate lamps
Plain purple is lights 'feed' and this is switched between dip and main on the stalk obviously.
Brown/Yellow is the main feed to the lighting switch, so take this to your switch.
Now the question, why? If the switch is dicky, get a can of contact cleaner from your motor factors, remove the switch, and squirt it into every hole you can find (on the switch!) working it all the time, I need to do this fairly often after the Lightweight has been laid up, but never fails to sort it, and keeps it sorted whilst in regular use.
Even replacements can be got for ~ £30 on ebay.