how can i fix my brake lights?

Wrong section cut paste to cars section.
Follow the tow hitch socket wires to the car connecton points and look see if one of the splice blocks has a wire missing of the colour you decribe as far as the sockets go it's not the 12n 7 pin harness colour they are all single colours so it has to be the stops wire they spliced in to to connect the tow sockets. check out the tow wire diagram/s by typing in google search type in search engine box 12n wiring diagram.
or try the site below if it works you'll see both the 12n [road lights indicators] and 12s [caravan auxillary] sockets.
www.tptrailerparts.co.uk/PlugWiringDiagram.html

BB
January 2010