I am trying to fit a third brake light in my 1993 nissan micra but am unable to establish what colour wire (in the cluster of wires going to the rear lights) is the wire i need due to nissan's habit of using different colour wires from usual.

Go up on your voltage on your fuse. If it still blows then you have a short somewhere in the wire chassis( I'd look around the back for any exposed wires that are being held down by zip ties; they can pull the shielding off of the wire chassis and cause this issue.

By the looks of it, there seems to be an Achilles heel where the rear hatch opens up. There looks to be an exposed wiring junction box or terminal around that area. Check and make sure your wires are not being exposed to any moving parts that could cause friction, which, again, will rub off the shielding and cause the short.

Hope this helps.

This fault is a bit srange, when you apply the brake pedal you here a
"Knocking" noise from the front of the car, alternating from one side to the other, the cause of this is a bad earth in the rear light clusters,
which results in the headlight motors activating "Jumping" thus causing the noise, solution is to clean the conections and conecting
blocks of the rear light clusters in extreme cases change the rear light clusters but a good cleaning should fix it hope this was helpfull

fuse or relay are all the wires correct at the bulb clusters make sure these are fitted correct and the bulbs are the correct type either single or double pole bulbs

The wires going into the right hand rear brake light has a red,green wire with a silver band. This is the wire that powers the 3rd brake light. Disconnect the wireing plug from the light fitting and meter out the red/green and silver wire from there up to the 3rd light, this will prove if there is a break in the wire ( most likely are is inside rubber grommets at tailgate hinge. ) This will prove the wiring. I got a spare piece of wire and ran a jumper cable from the silver track on the light fitting relating to the green red and silver wire ( top left track ) to the light fitting and another wire to earth, activated the brake and the light came on proving a break in the wire.

The lights get power from somewhere else, not their control button - you will need to access the wire connector at the left cluster and locate the wire that delivers the power and the status of the grounding connection/bolt (most likely it's corroded). Since the cluster of lights above the rear window are the central brake lights only it means that if you get them constantly on then the brake lights are constantly on . To check for that is easy, just test the brake pedal switch.

Go into the boot and access the tail light clusters under their covers in the boot rear corners. Take a lead (you can buy double adapter spade connectors) from (1) a tail light, (2) a brake light, (3) the right indicator, (4) the left indicator. (5) a solid earth wire. Try using different colour wires, making a note of each source and each corresponding colour. Tape them together and lead them to the trailer plug. There is a set international configuration for the trailer plug connections which is shown below.

right iam trying to re size a picture of the colours and iam posting it as a picture ,if it works

Hi There. Im not sure where you are but this is the sequence for the UK< Hope it helps.
here are the 7 cable locations and pin numbers.
Pin 1 Yellow L/H Direction Indicator
Pin 2 Blue Rear Fog Lamps
Pin 3 White Earth Return
Pin 4 Green R/H Direction Indicator
Pin 5 Brown R/H Tail & No, Plate Light
Pin 6 Red Stop Lamps
Pin 7 Black L/H Tail & No, Plate Lights

I found the easiest way to locate the correct wires in the loom is to turn on the lights required and use a circuit tester and splice into the main loom where you have enough wire to play with. Try not to cut the loom as it only causes more problems with bad connections and joins.(
Good Luck

if you are putting an after marker stereo the wiring is different from a stock radio some audio stores sell adapters for after market stereos that you jus clip on to stock wiring

check your rear luses has a short or come together the wires