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Discussion Starter · #1 ·
Hi would appreciate some help trying to fix an issue that has been about in my partners car for a long time, the interior light doesn’t go on when the door is opened, or when the car is stopped, or unlocked. It does work on the overhead switch set to the on position, just not on the door setting in the middle of the 3 way rocker.

As it’s not the bulbs, i thought it was the switch, so I have a b8 a4 myself and swapped the overhead light panel, but this didn’t fix it.

Next up I had a thought it may be the door open trigger, but this shows on the display for both doors, and then thinking about it from my vehicle it does work on unlocking and also whenstopping and removing the key.

I’ve had a shot of a vcds cable, with no relevant errors I can see, but not sure if there is any further tests I can runwith that.

I can’t remember them ever working, the car had the mmi headunit out for months as It had failed on an update, and took a long time to send it off to get fixed, so I thought it was related to that missing, but can’t really remember if they worked before? Now the mmi is back and working and the lights aren’t fully I doubt it! The only other thing I’ve added is ambient lighting, not sure if this would affect it?

I’m guessing the overhead lights aren’t getting a signal from the trigger wire, unsure if it’s canbus or not? Possibly from the j519 if that controls it? I don’t have any wiring diagrams, so anyone with any knowledge or links to them would be hugely appreciated, and any explanations would be great too. I’ve double checked every fuse I can find, but was thinking it should be ok as the light works in the on position, if it’s not on a different fused circuit? If anyone else has had similar issues I’d appreciate any ideas, as I’ve tried as much as I can with my own ideas, but stuck now! Thanks in advance.
 

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The BCM/CECM J519 operates overhead interior lights directly:
Product Rectangle Slope Font Parallel


J519 terminal T17l/9 appears to power lighting in the "door" position, while T17l/17 powers all interior lights (vanitys, glovebox, overhead, etc.). You said above that you swapped the overhead panels -- did this one work in your B8 A4? I think I'd look at power from J519 on terminals T8b/4 and T8b/7 (constant at pin 4, switched at pin 7). --g
 

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Discussion Starter · #3 ·
The BCM/CECM J519 operates overhead interior lights directly:
View attachment 182359

J519 terminal T17l/9 appears to power lighting in the "door" position, while T17l/17 powers all interior lights (vanitys, glovebox, overhead, etc.). You said above that you swapped the overhead panels -- did this one work in your B8 A4? I think I'd look at power from J519 on terminals T8b/3 and T8b/7 (constant at pin 3, switched at pin 7). --g
Hi thank you so much for taking the time to look this up. And get back to me. Tried to decipher it as best as I can!
Yes both panels worked perfectly in the a4, neither one the a5. Will check the blue wire J519 terminal T17l/9. Will also test the T8b/3 and T8b/7 (pin 3 and pin 7 now I see how that is deciphered thanks!) for power in switched and constant, there are 5 plugs in the j519, can you point me in the direction of you know as which one is the t8b before I go try the pins 3 and 7 in them all?! Thanks again
 

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OK, so the A5 panel is confirmed good/working.

I would start at the flat 8-terminal T8b connector in the roof:
1: open
2: open
3: Green/Blue (control illumination)
4: Red/Yellow (to J519 T17l/17) constant 12V
5: Brown (to ground)
6: White/Blue (to mirror)
7: Blue (to J519 T17l/9) switched 12V
8: open

The smaller flat 4-terminal connector goes to the rear overhead light fixture. Both connectors on left side facing forward.

J519 connector T17l is A1 in the diagram:
Automotive design Motor vehicle Font Automotive exterior Technology


Good luck --g
 
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Discussion Starter · #5 · (Edited)
First off, thanks again DrGer for your time and effort to explain and send through the diagrams.

I decided to stay up late and have a go, outside in the frosty night! I tested the t8b, pin 4 constant voltage was fine (manual on off), pin 7 switched power showed nothing. My t8b was slightly different with a grey blue at pin3, and no pin 6 to mirror.
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At a loss, I Decided to take out the j519, not the easiest to get to, but I wanted to check the pins as I had previously retrofittedfootwell lighting, but they were all correct. I then decided to remove the j519 and take it apart, to check for any damage or burnt electronics inside. All I noticed was some tarnishing on mainly the bigger pins of the 17 pin connectors. I gently gleaned these with a wire brush on the dremel. When it was refitted I tested pin 7 but couldn’t get a reading, so decided to plug back in the lighting panel. I had also traced pin 3 of the t8b back to a5 or a7 in the j519. This was now testing as 0.1v with the door open and dropping to 0 after being closed for a few seconds. I plugged connector t8b back in and the lights worked on the door open setting.
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Since my partner purchased the car over 3 years ago, there had been a strange electrical fault, where the battery would drain rapidly once the car was turned off, but not locked, the fuel pump kept cycling, like it was continually waking up every 20-30 seconds. Once locked everything went to sleep and it held charge. I’d spent hours trying to do parasitic draw tests, struggled to find a garage that would deal with a strange electrical fault, and was at a dead loss as to how to solve it with no relevant errors in vagcom, and no one had any ideas in a previous post. Due to this I had to run a large charger on the car anytime I was working on it, to counter the drain. I noticed the chargers fan had stopped a little while after removing the j519, meaning it had gone to the second charge stage, as it was not fighting the drain. Once the j519 was back in, the car stopped its frequent fuel pump priming! I can’t tell you how ecstatic I am about this after so long! My guess is a poor connection in the lights or another connector in the j519 caused the car to continually wake, and that drained the battery.

Now she has working interior lights from unlocking the car, and (fingers crossed) no more random drain with the engine off! Delighted, thanks to DrGer, and hopefully someone else reading this may have success with solving niggling electrical faults by cleaning up the (slightly) tarnished j519 pins.
 

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Hey thanks for the excellent feedback and lets see some pics of both cars please!
 

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Discussion Starter · #7 ·
Thanks Simon, I thought I would update it in case it helps anyone else out in future. Here are his and hers 3.0 tdis, not always to everyone’s taste!
Wheel Tire Car Vehicle Hood

Tire Wheel Land vehicle Car Vehicle
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Yeah, I'd settle for a stock B8.5 A4q Avant TDI 6MT over here... --g
 

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Discussion Starter · #9 ·
Yeah, I'd settle for a stock B8.5 A4q Avant TDI 6MT over here... --g
Yes they are both b8’s with b8.5 conversions, bought both cars already modified, I was going to remove the wrap on mine but it has grown on me. I’ve not taken a liking to air ride though. Think my next purchase will just be stock.
 
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