Re: Faulty brake lights..
Just to add my experiences (2000 spider, same problem, lacking diy/mechanic skills)
I filed off the switch as described, tested it, much the same, filed off more (too much) - discovered the plastic is hollow - thus make a hole from which a spring flies out across the room. Curse ++.
Then go to alfa dealer, get new switch for about a tenner, problem solved, much happier brake lights now work.
Was previously contemplating trying to fix my juddering intermittant wipers, but will give up and ask the garage to de-grease instead (see wiper problem thread)