Inner tail light led fault

[redjoe100]

Hi, my rear inner/boot passenger tail light led does not operate, I also get a warning on the dash.

I removed the cluster, cleaned it up but nothing is obvious. The bulbs in the cluster work.

Does any one have any suggestions for repair or where I can find an affordable replacement?

Thank you

[cliffcoggin]

It would be worth checking the wires in the boot. They have been known to get damaged.

[redjoe100]

Thanks Cliff, I swapped the faulty side over to the working side and get the same fault, vice versa and the working side fails on the other side. I'm almost certain it's the circuit board or less. Do you know if they can be repaired or parts ordered at that level. Cheers

[cliffcoggin]

Sorry, I have no idea.

[redjoe100]

Hi all, I've got a real head scratch going on with my inner/boot hatch tail light.

The reverse bulb works but the led surround strip does not. I removed the passenger side and plugged it into the working driver side....the led did not work so I assumed it was the led and bought a new cluster 🙂

The new cluster arrived but did not work in the passenger side or the working driver side so I assumed I bought another broken led cluster 🙃

To double check I put some voltage across the pins in the connector and the LEDs work in both the original and new passenger clusters!🙂

This leads me to believe its somewhere further down the chain and that the passenger and driver side connector pinouts are different presumably because the clusters are mirror images of eachother and the power strip runs have to be different?

Does anyone have any experience here or perhaps a pinout or wiring diagram so i can confirm this?

The information panel on the dash does alert me to the faulty light but im guessing it doesn't know the difference between a blown bulb and a fault elsewhere in the cable?

Any help appreciated!

Thanks

[Magnet]

Hello Joe,

Peel back the flexible harness cover over the section of harness between the body and the tail, and look for any wire breaks or partial breaks, just to eliminate that possibility.

Kind regards,

Gareth. 

[redjoe100]

Thanks Gareth

I've removed some of the inner trim and panels to access the harness, carefully removed the wrap but as far as I can tell there is no damage. Any idea what to try next? Thanks again

[redjoe100]

Thanks Gareth

I've removed some of the inner trim and panels to access the harness, carefully removed the wrap but as far as I can tell there is no damage. Any idea what to try next? Thanks again

Update: found no cable damage after digging into the boot lid and where the loom enters the roof void (checked the rubber hinge boot too). I then focused my attention to the same side but outer/main light....cleaned that and it's connections up. Now the dash warning has gone and the outer light led strip illumates partially. So some progress.

Still no inner LED surround but the fog and reverse lights do work. That means 3 of the 4 wires are fine and have power but the 4th (for the LED) is faulty. Any idea where that's powered from or which one of the wires it is?

Thanks

Edited May 17, 2020 by redjoe100
More photos

[Magnet]

Hello Joe,

My guess (but a guess it is) that this problem is plug connector associated. Where? If it were mine, I would be investing in some spray on contact cleaner and giving everything a good old squirt - including the fuse contacts. 

At least you are getting somewhere. Well done.

Kind regards,

Gareth. 

[redjoe100]

Thanks Gareth, some spray on order. Will have another attempt soon and post back. Cheers

[cliffcoggin]

The pins in that connector look a bit crusty. I'd try a bit of fine abrasive before the spray cleaner.

[redjoe100]

Thanks cliff, I did run a small piece of scouring pad over the pins, that's what for the outer light LEDs working (albeit dimly). I'll have another go before I apply some spray.

Does anyone know if the inner LED is fed from the outer LED cable? The seem to illuminate at the same time on the driver side .....if that's the case it could be the wire that links them.

Thanks again

[redjoe100]

Manage to get the bottom of it after alot of faffing around...

My inner/boot tail light LED wasn't working because it's live feed is taken from the live feed on the outer tail light. The outer tail LED driver board had previous water ingress causing that LED to partially illuminate but not enough to notice it was at fault (at first). The LED driver board was also not outputting enough juice to supply the inner LED.

I took the lights out and because I couldn't find a wiring diagram I buzzed out and took the voltages across the contacts, that gave me enough to know that outer LED feeds inner LED so I buzzed out those link wires (marked in blue in the picture)....all good apart from lack of volts on the passenger side.

Anyway, replaced the entire outer cluster on the passenger side which now kicks out the correct voltage to the inner and happy days!

If anyone is interested I've attached my scribblings for my variant of A3. It shows the cable colours, connector pins and continuity between ground and live with lamps inserted. (with cluster and bulb housing removed from car)...hope it helps someone out.

Thanks for all the suggestions

[cliffcoggin]

Glad you got it sorted out, and glad too that you analysed the problem and reported back. It may help others to know what a water leak can do.

[Steve Q]

Glad you got sorted 👍

[Nic87]

I have exactly the same problem, I have ordered the outer cluster in the hope it solves the issue after reading this. I also got a new cluster for the boot. I was so puzzled why it wouldn't work and would never have thought it might be to do with the outer cluster. I read this and had a light bulb moment (ha) when I realised the outer cluster must have water ingress too because it has condensation, it's still lighting up (just dimmer and a bit flickery) fingers crossed 🤞🏻

[cliffcoggin]

And thanks again to Joe for his analysis which I have marked as a solution.

[Nic87]

New outter cluster arrived today, low and behold both now work and my sanity is saved! Thanks so much for sharing

[FJM]

Hi there

2014, same issue, replaced inner left and still not working

Right corner light delivery pending

kind regards, FJ

[FJM]

Hi there

2014, same issue, replaced inner left and still not working

Right corner light delivery pending

kind regards, FJ

[FJM]

So fitted left outer, 2nd hand, no change. All connectors on both inner and outer and wires look good, no water damage obvious.

Anyone have any ideas?

kind regards, FJ

[Rybrook]

I had similar with my number plate lights, one side was working but dim and not the other, changed the bulbs and both didn't work.

Checked the cable gland, no breaks. Defurred the brass contacts and still no light.

Stripped the boot lid to remove the switch. Refitted the the lights with unit in hand.

Stuck a 12v incandescent brake bulb onto the connector and it lit up when pedal was pushed.

This tricked the bcm so it got full voltage to the switch, then refitted the switch and both lights were working.

 

I still think it was green crustyness on the contacts.

[FJM]

Thats fair enough but connectors, lights are clean dry, no evidence of overheating, corrosion etc. Mystery continues