electrics Common Fuse for Reverse, Fog and Number Plate Light and Boot?

[drewwwwwd]

Hi Folks,

As of yesterday, my 2008 A3 Cabriolet warns me that the reverse lights, rear fog lights and number plate light are out of action. Also, the key fob won't open the boot. And every time I brake, the rear parking sensor beeps - and this is while going forwards. This stinks of an electrical fault, and apart from the braking/parking sensor thing, sounds like a burnt out fuse. The only thing is that my manual doesn't seem to mention the rear lights or boot catch in the fuse table, so I've no idea which one to check. I've included photos of the relevant manual pages, in case I'm pretty going mad and failing to read properly!

Anyone got any clue what I can check? Or what fuse this would be, if they all go through a common fuse?

And all this only a day after I got a safety recall notice about the car!

Cheers, Drew

[cliffcoggin]

I'm no electrician but it sounds to me more like a bad earth.

[drewwwwwd]

Cheers Cliff, do you reckon this is something my local garage could have a stab at or is something better suited for a main Audi service centre? I've never really had any problems like this on any of my cars, only more clear-cut mechanical problems. I've have had mixed results with local garages, but then the proper Audi garage will be about twice the price!

[cliffcoggin]

Main dealer, local garage, auto electrician: you pays your money and you takes your choice. It depends on how competent they each are, and I really can't judge. If you car is being recalled to a main dealer for other reasons I suggest letting them test the electrics while there, then decide what to do. Is it possible the recall is because of electrical problems?

[Scotty D]

An old post I appreciate but wonder if you solved this, I have same thing happening. Read somewhere else that taking a live feed from battery to reg plate bulb will solve but not tried yet. Apparently doing this with the live wire “reminds” the ECU that it should be sending power to the boot lid. Sounds odd but worth a go I’d think.

 Thanks 

[Magnet]

Hello Scott,

Before doing any bodges, check for breaks  in the wiring in the fluted rubber section where the harness runs from the body to the boot. Quite common for there to be issues there, due to the flexing of the harness as the boot is openes and closes -  particularly in cold weather, when the wires become more rigid. 

Perhaps you could let us know how you get on.

Kind regards,

Gareth. 

[Scotty D]

So, i have fixed it, problem was a broken wire after all, one of the wires inside the black rubber gaitor/sleeve that goes between the body to the boot lid. It had been repaired in the past and was the thicker brown wire. I didn’t see this on first inspection as the repair was good being done with solder so I thought the chances of it having broken again were slim - a wrong assumption on my part. Having gently pulled at the wire, I was delighted when it came out one end broken as I knew then that it was mystery solved and an easy fix. All lights working together with boot lid release button which is working from key fob too. 
Thanks for the input and happy motoring. 

[Magnet]

There we are Scott. So you’ve learned something new today then!

Glad the forum was able to sort it for you. 

Bodges are bodges, fault finding is an art! 

Kind regards,

Gareth. 

 

 

[ncr]

Just signed up to say thank you! This thread was the solution to my problem as well 😄
Same exact car as Scotty, and the same wire broken in the same spot:

 

I pulled it out, threaded a new one through the sleeve, reattached the ends with terminal blocks, and everything was fine.

Basic stuff for anyone who ends up here in the future:
- Yes, the sleeve can just be pulled out of its socket using enough force, and squeezed back in.
- You can open the boot mechanically using the key. The hole is right next to the boot button.

(The latter might seem obvious, but in another thread, the discussion revolved around crawling in through the back seat rests to troubleshoot.)

 

 

[cliffcoggin]

Thanks Erik. It is good to read that the forum has provided a solution for you.

[Stagn8]

Just as an aside, soldering wires seems a great solution but with movement the brittle solder will crack as mentioned in one of the above posts. A better solution is to mechanically twist the wires together and then cover with heat shrink tubing to keep it all together. This way movement can be incorporated without risking further breaks.

[cliffcoggin]

That's a good point about a soldered joint possibly breaking as it flexes, but wouldn't a twisted joint also become unravelled when flexed and vibrated despite being covered with heat shrink tubing? I have a deep distrust of twisted wire joints, and have always felt a soldered joint to be more durable.

[Stagn8]

It’s all in the twisting Cliff 😀! 
I was in electro-mechanics for many years and had many solder failures (dry joints, fractured joints, high resistance joints, so not a fan, though have used on occasion) as a good solder joint depends on a fair amount of skill along with the correct flux, iron etc. So, for the average Joe mechanic a twisted joint with heat sleeve is reasonably simple and reasonably fool proof.
There are some superb in line jointing devices available these days including ones which shrink and have a bonding agent to make them waterproof but of course you need to have them at hand before discovering the need 😀. 
If there is sufficient slack in the loom to allow for a loop and a reduction in the stress of opening and closing then both methods would have equal merit but if the loom is a bit on the tight side then careful consideration will be needed as to the best solution and perhaps an extra bit of cable will need to be spliced in.

Edited January 10, 2022 by Stagn8

[ncr]

Piggybacking on the already derailed thread, any thoughts on using simple terminal blocks? 😁

(Pic attached, in case that's not the correct translation.) 

[cliffcoggin]

I would prefer terminal blocks if there is space because I am unconvinced by Keith's advocacy of twisted jonts. I have seen too many twisted joints fail on cars over the years. However in this particular instance I do not know if there is space for such a block. Either way some slack in the wire, or even better a loop as Keith suggests, would relieve the strain from repeated opening of the boot.

I am not an electrician but mechanical locking of two wires together with screws or solder were the only acceptable methods of joining or terminating wires in all my years in industry. The same applies to domestic electrical installations from what I have seen, though spring loaded blade connectors like the Wago are becoming popular.

[Stagn8]

Different experiences lead us all to different preferences 😀 and of course preferred solutions. Terminal blocks work well and I believe from the picture that is what has been used, wrapped in tape for extra protection and most importantly with  a loop to remove strain, without that the movement will pull the wires out quite quickly. My beef with them is the difficulty of getting all the strands neatly into the block and once you have tightened the screw only a few wires will actually be under the screw and secured so overall quite a weak join.

House wiring is all single core and doesn’t move, soldering, wago, terminal blocks all work well, it is multi strand that causes difficulty.

Sorry to derail thread but my own view is that shared knowledge and experience along with discussion, if relevant, should be the backbone of a good ‘forum’. Perhaps I am wrong.

[Magnet]

As Cliff points out, ‘choc blocks’ as I call them are used (where absolutely necessary) on domestic electrical installations , so are capable of handling voltages and currents beyond what would be encountered on auto electrics. So in my book, they are fine to use - if space allows. 
Taking Keith’s point about strands of wires straying away from the actual terminal bore, then I overcome this by first soldering the stub end which then fits nicely into the terminal, and provides a good gripping area for the terminal screw to bite into. 
Crimp terminals? Now there’s a different story, and personally I don’t like them, based on too many becoming detached, despite using the correct crimping tool. If it turns out it is a must to use them, then again I solder the ends of the wires to improve the bite. 
Kind regards,

Gareth. 

[Stagn8]

Great advice to solder before using these devices Gareth.

[cliffcoggin]

9 hours ago, Stagn8 said:

Sorry to derail thread but my own view is that shared knowledge and experience along with discussion, if relevant, should be the backbone of a good ‘forum’. Perhaps I am wrong.

I see it as very relevant to the thread so no apologies needed. It's always good to consider different views even if there is no concensus.