Will1893

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So I've struggling to find the cause of some problems for a while now. The car is a 2005 A3 3.2 V6 Quattro Sport 8P1.
Here are problems and some information:

Reverse light doesn't work (bulb is good, no warning on dash, when I put in a new bulb a bulb out warning came up on the dash so I replaced with the original bulb and again no warning on dash but not lighting up).

When the headlights are turned on:
-Bulb warning light for right rear light on dash (even though the light works).
-Bulb warning light for right rear turn signal dash (it flashes fast like the relay has gone on the dash but flashes at normal speed on all lights on the outside of the car).

When I leave the car still for 3 days the battery is completely dead and needs jump starting. Otherwise the car is fine if driven daily. I've already replaced the battery.

I took some time looking today and found 3 ground points in the boot. 1 under the polystyrene that connects directly to negative battery terminal and 1 under each C pillar, I cleaned up all ground points.

Now when I took the tail lights off the car I noticed a wire had been spliced into just before the connector to the light, it went behind the rear bumper so I followed it and it connected to another spliced wire just before the other tail light connecter.

I disconnected the wires and joined them back to how it should be. Now either my battery is dead (quite likely as I did have to jump start this morning and only took it for a 20 minute drive) or it's now not completing a circuit somewhere I assume. Have to wait for the other half to get back from work so I can try jump start again, the tension is killing me.

When looking at a wiring diagram the wires that were spliced in to were the rear lights. So somebody just connected the rear light wires together. Anyone any ideas why someone would do this? Might help me understand what's happening.

Any information and opinions are welcomed!!

Few photos:
view

view

view

https://drive.google.com/file/d/1_gx41UI5gRJ5EgSrRO0WtyhQI9O0s09k/view?usp=sharing
https://drive.google.com/file/d/1_qF_oAbc-K0QuO8BtDj56nSem9G1U_YN/view?usp=sharing
https://drive.google.com/file/d/1_rh47puiGALKEWJdux9S0Ar5ZWQj6TUl/view?usp=sharing

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abmat

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Battery could be duff or your alternator is on its way out.

as for why someone would splice into the rear lights I don’t know. Unless they were a numpty and it had an aftermarket alarm and they meant to splice into the indicators. Do you have any led bulbs fitted?
 

Will1893

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Yeah I was thinking it might be alternator, I replaced the battery for a new one so would be surprised if its that but I wont rule it out..

I know it's very strange. No they're all stock lights, no xenon or halogen head lights either just the standard two bulb.
I'm suspect somebody was trying to fix this problems already by connecting the tail lights but I have no idea why.
 

abmat

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Sounds like someone was trying to link one side to the other as one wasn’t working.

check the output voltage on the alternator, should be >14v. If that’s fine then is a matter of going through the fuses one at a time to see which circuit is causing a drain.
 

Will1893

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Sounds like someone was trying to link one side to the other as one wasn’t working.

check the output voltage on the alternator, should be >14v. If that’s fine then is a matter of going through the fuses one at a time to see which circuit is causing a drain.
Yeah that's what I'm thinking, I guess one of the tail lights wasn't working in the past.

I'll have to wait until the morning now to see if it will start with the wire removed.

Do I test output voltage by putting multimeter on battery terminals with engine running?

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abmat

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You can do.

I’m ashamed to say I own the same car as you but don’t know where the alternator is. Think it’s on the underside of the engine.
 

Will1893

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So it started up fine when I jumped it.

The Reverse light had a bulb warning initially, but then went and it's still not working
However all the other bulb warnings have disappeared which is some good news.
I also forgot to mention that the boot/luggage bulb isn't working.

I started the car and the lowest voltage on the battery terminals I could get is 14.1-14.2, that's with everything that could be turned on was turned on. So that would imply that the alternator is still good I assume as it's higher than 12.6v?

I'm getting a battery charger later and will put on charge overnight so its fully charged then I'll start testing for a drain and pulling fuses. I'll check if there's power to the reverse light and boot light too.

I was also thinking it might be the reverse light switch on the gearbox, but with the boot light being out too I'm thinking that's unlikely at the moment..
 

abmat

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The luggage light terminal is quite flimsy and snap easily. If not that could be the switch
 

Will1893

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I charged the battery overnight and started testing this morning.

The battery was as it should be 12.6V
I then did a drain test with multimeter set to 5A setting and connected to the positive battery terminal, and the positive battery lead.
When connected the amps shoot to 1.1 then down to 0.9 where it stays for a couple of seconds then goes down to 0.4 where it stays. I think I'm right in saying that 0.4a drain isn't enough to drain the battery and pretty standard.

So I don't know now. Maybe the battery is broken but its only 6 months old and the same thing was happening with my last battery. Maybe something is damaging the battery and causing it to lose charge very quickly, I'm not sure.

In other news I got my boot/luggage light working by messing with the bulb holder and trying new bulbs (even though the bulb that was in there was good and tested). However the reverse light is still not working so I'm going to assume as now I've got the boot light working, it's probably the reverse switch on the gearbox. I'm going to order one now.
 

SootySport

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It may have had a tow bar sometime in its life, put the wiring back to stock and see if it helps.
 

Will1893

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It may have had a tow bar sometime in its life, put the wiring back to stock and see if it helps.
That's a good shout I didn't think of that.
I've already put all the wires back to stock and that's fixed the bulb warning messages on dash I was getting.
But the reverse light still isn't working, I tested the reverse light wire on connector to the cluster and it read 0.6v which was the same as the other working wires so it's getting power. My next guess is that it's the reverse switch that connects to the gearbox, I've ordered one that should come in the next couple of days and I'll report back.
 

Will1893

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I replaced the reverse light switch, no change still not working.

I realised today that when doing my test for a draw on the battery my conversion between milliamps and amps was wrong. 0.4A is 400 milliamps which is a significant draw on the battery. From researching I found out it should be around 30 - 50 milliamps. So I decided to retest earlier.

This time I turned the car off, clicked in the boot and door switches as I had these open for access to fuses and didn't want the car to think they were open. I then let the car sit for about 30 mins to fully shutdown anything that might still be working and began testing.

The draw from the battery this time read at 0.1A which is 100 milliamps, still a significant draw.
So I began pulling fuses one by one until the reading dropped.
And it did when I pulled out Fuse 3 from the engine bay fuse box, it dropped down to 0.05A.
From studying the wiring diagram this circuit contains the "convenience control unit", which I believe controls the central locking (which funnily enough started acting up today).

So I've ordered a replacement control unit, I'll replace that and see if it makes any difference.

I hate electrics.
 

Felix B

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Did you get anywhere with the reverse light? Sounds like I've done all the same tests you've done and still can't find the problem.
 
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