You need to source the wires going to the tail lights. Purchase a 7 pin plug which will have the information you need.ie. What functions go to what number in the plug. You will need to tap into the original wiring so you can "T" into it. Most towbar installers use "scotch locks" some call them "quick tees". Most of the time you only need 6 core cable as the 7th pin in the plug is for trailer brakes which you may not need. The six you do need is right and left hand indicators, tail lights, brake lights, reversing lights and the earth wire. You may also need to use a test light or multimetre if you are not sure which wire does what function. Otherwise you will need to trace each wire to each bulb to work out their function.
John, June 2005