What exactly did you do? Is that the translucent red tape or a piece of plastic or what?
I have been looking and waiting for years for some decent tail lights to come out for the Ti, they seem to have them for every other bimmer. I recently hit the jackpot tho at a German website..
www.germanstuff4you.com Just do a search for 318ti there and the lights will come up, they have a nice selection. I'm not sure about the quality tho, since I haven't ordered from them yet.