The new taillights are equipped with a contact plug that is inserted into the bulb holder. This contact plug is keyed, so it can only be inserted when properly oriented. Just push it all the way in until it won't go any further. Then insert the holder into the new taillight and twist until it clicks in place. Put the new taillight in place, insert the two Torx screws removed initially and tighten. Repeat the process for the other three taillights and you're done.