You can get an illuminated Cig Lighter from Halfords for about £7.00. The come with three wires - two red, one black. The black is your 'ground' or 'earth' - just connect it to the earth connector on the cig lighter wiring thats already part of the wiring loom. The first 'red' is connected to the remaining existing cig lighter wire of the wiring loom. The second red is to connected to the bulb that creates the illumination, and is connected to any lighting circuit that is only 'live' when the ignition is 'on' and the h/lamps are on. This part is important because if you connect it to any old wire that is live, it will drain your battery eventually. Ideally, it should be connected to a fused lighting circuit and all work should be done when the battery is disconnected as a short circuit can sometimes be a very expensive mistake if you have connected it to the wrong 'live' wire.