Hi all,

My third brake light doesn't work. The other two at the rear do. Any help would be appreciated as the car has an MOT coming up over Xmas which it is going to fail if I don't sort.

So far I have tested the circuit and found there is no continuity to the ground pin, and if I force an earth to that pin I do not get any voltage to the live pin. So neither pin has much going on...? Does anybody know where this should be grounded?

I have stripped back the trim at the back passenger side to find no wiring issues that I can see. I have removed the ground here and cleaned up etc. Should I be completely stripping the wiring covers (tape/rubber etc) back to trace it? Are there any key areas where the wiring might have been shorted etc?

I have checked all of the fuses in the dashboard fuse box and they are ok.

As I understand from reading the forum it is on a different circuit to the other rear lights (why?). I believe the issue could be the body computer (where is this?) or the brake pedal switch (but if the other two lights work I do not think it would be the switch).

In possible connection (or lack of!) the dash warning lights are telling me the boot is open even though it is not and the boot catch release works as I can hear it engaging and disengaging.

Have I missed anything? Any advice would be great!

Thanks. Josh.

jjt888 said:

Hi all,

My third brake light doesn't work. The other two at the rear do. Any help would be appreciated as the car has an MOT coming up over Xmas which it is going to fail if I don't sort.

So far I have tested the circuit and found there is no continuity to the ground pin, and if I force an earth to that pin I do not get any voltage to the live pin. So neither pin has much going on...? Does anybody know where this should be grounded?

I have stripped back the trim at the back passenger side to find no wiring issues that I can see. I have removed the ground here and cleaned up etc. Should I be completely stripping the wiring covers (tape/rubber etc) back to trace it? Are there any key areas where the wiring might have been shorted etc?

I have checked all of the fuses in the dashboard fuse box and they are ok.

As I understand from reading the forum it is on a different circuit to the other rear lights (why?). I believe the issue could be the body computer (where is this?) or the brake pedal switch (but if the other two lights work I do not think it would be the switch).

In possible connection (or lack of!) the dash warning lights are telling me the boot is open even though it is not and the boot catch release works as I can hear it engaging and disengaging.

Have I missed anything? Any advice would be great!

Thanks. Josh.

Click to expand...

hiya mate ..same happen to mine a year ago! just stopped working (bad fitment i' guessing) took it to FIAT who replaced it ..it cost £60 blah blah

Cheers for your reply Ame.

They replaced the light itself? Or another part?

Thanks. Josh.

jjt888 said:

Cheers for your reply Ame.

They replaced the light itself? Or another part?

Thanks. Josh.

Click to expand...

they replaced the whole light ..i know other people who have had the same problem!

my light rotted internally

before you do that get a 12v test light and prove out the wiring...

I'd open the boot, find the rubber sleeve linking the boot door to the car and pull that out both ends.
Then check the wires going through it, I had trouble with the boot catch not working and the rear heater not coming on. Turns out two of the earths into the boot had snapped and the earth along with the interior light earth!

Where are these earths? is one the looping black wire thats on the connector of the third brake light?

Hi Gimba,

earth cable should be connected to the chassis @ C030 ... and is a black wire. You can test your 3rd light with a simple 9v battery, wouldn't destroy anything.
No boot opener, no heater, no 3rd light > no earth (how about the wiper) ??

Regards, Bernie

BTW, have checked eLearn, the 3rd light wire is orange/black, here some screen captures that may help...

Regards, Bernie

ever seen the thanks icon ?

3rd light works, wiper works, not sure about heater because no ice to test melt, lock doesn't work, makes a clicking sound in the dash, but doesn't open or any noise from the lock itself

You hear the relay in the dash (actually in the Body Computer), but the power doesn't get thru the boot opener, here's the drawing, hope you can read it... if not, tell, and I'll explain...

Regards, Bernie

BTW, wasn't this thread about third brake light originally ??

3rd lights, wiper, heater and locker are separated and they share the same earth point WITH SEPARATE WIRES (or maybe shared in a certain way) , You have to check and fix any issue here !!

What does this black wire connect too
I have the black I'm in the connector along yellow, but this black looping one doesn't look like it's connected to anything :/

Also I don't understand any of those wire diagrams you post lol

:bang::bang::

I will make you a clear description of the drawing tomorrow, heading to bed right now.

BLACK wires are 99,99999% of the time ground wires, so they're connecting , say like plastic 3rd brake light assy, to the car's chassis (negative pole of battery) and the On Board Controller, being simple switch or Body Computer, provides the positive part to the device (in this case the central brake light) USUALLY thru a fuse and a control switch (or body computer's relay) .
One of them missing (disconnected/broken/roten...) and the device stops functionning...

Regards, Bernie

Hi Gimba,

can't make a better description than eLearn...

Regards, Bernie

Thanks
But been told it could possibly just be so you can pull the connector through to the other side

the connector itself is already wired up with a black and a yellow and black wires
This looping one was just looping on itself, not connected to anything

hmmm, let's start with the basics then...

in order to lit a bulb needs some energy to pass thru it that would warm-up the filament hot enough so one can see it. On cars, this (electrical) energy comes from and returns to the battery by means of wires. On older cars one of those wires was the car itself (as it is made of steel it conduct electricity) so most of the electrical equipment only needed one wire (the other being the chassis). Nowadays with more and more plastic coming in the cars, less and less devices are happy with one wire only and therefore one need to feed them with two wires. One being still called "ground" or "earth" or "la masse" in French, and the other coming from the battery positive via a switch, a relay or a SS device in the body computer. One of them getting broken, the device would not function anymore since the circuit being "open", no energy can flow thru...

Your picture is not clear enough so we can distinguish how the connector is fitted but I'm pretty sure the black wire (loop) actually need to be grounded (the chassis is still connected to the battery negative) and the yellow/black (should be orange/black) is carying the positive. Connect a 9V battery block to the terminals on the 3rd light and it should lit dimmy... If ok, you should restore the connections as they should, from the 3rd light to the chassis earthing point (left rear wing) via the rubber @ hatch hinge and to the body computer (below glove box in UK) for the positive wire.

Hope that helps, regards, Bernie

My light works btw
Just confusing what this black wire is for (its a spare, there is already a black wire connected in the connector along with the orange/black wire), but i reckon it's to pull the connector towards you when feeding it through the gaps

Italian design ? :worship:

Is you locker working finally ?

Regards, Bernie

Nah that's still rubbish and not working
Checked the fuses they're all good (cant access dashboard ones though)
But going to check to see if the current is going through to the lock over the weekend, if it does then hopefully its just a case of changing it over

"Checked the fuses they're all good (cant access dashboard ones though)"

By Murphy's law, the blown fuse WILL be located in the dashboard (F73). BTW, why can't you access the body controler ?

Regards, Bernie

Oh you're joking lol, damn, it's got a big metal bracket frame that cant be moved, I just need longer pliers but I just don't have them