B6 A4 License/Number Plate Light Out Mystery

**amuletA4** · 03-05-2011 03:34 PM

So after searching on previous posts and not finding a definitive solution, I thought I would post the mystery of my light out problem and see if anyone out there can help.

I have a ’03 1.8T A4 sedan. A few weeks ago I got the “number light out” warning. I checked the lights and yep, they were indeed not functioning. So I go online and order some replacement bulbs. Those bulbs arrive a few days ago. I remove the old bulbs (gotta love those terrible screws, which I replaced with some new ones from Lowes, M3-.50 x 10) and put in the new bulbs. The new bulbs do not light up. I looked at the connectors- they are pristine, no corrosion, no rust, look brand new. I bent the connectors on the assembly and housing, still nothing. Then the bulbs work to my surprise, but only infrequently and intermittently.

As of now they do not stay on at all, except when I first turn on my lights- the right bulb lights up, then flickers and dims out to nothing after about 5-10 seconds. Coincidently, there is a “hissing” noise coming from the trunk lid that continues until the lights go out. I took a voltmeter to the connectors and it shows no juice is flowing after the lights go out. I have checked all the fuses in the driver’s side fuse box- all are good. My key fob will pop the trunk, no issues with trunk lock, and no other lights are out. I’ve giggled the wires in the trunk lid and the rubber section exiting the trunk lid- no change to the lights.

My best guess is there is a short somewhere in the wiring harness or in the light/trunk handle assembly or there is some hidden fuse/relay that is dying a slow annoying death.

Does anyone out there have the same problem or better yet know of a hopefully inexpensive solution?

Thanks,

- Jake

**michgo** · 03-05-2011 03:50 PM

The material of the screw the same? I went through this recently too and those little screws play a HUGE part in whether those lights turn on or not.

I actually have my spare light frame if you cannot get yours working too

**sa_seahawker** · 03-05-2011 04:27 PM

Originally Posted by michgo

The material of the screw the same? I went through this recently too and those little screws play a HUGE part in whether those lights turn on or not.

I actually have my spare light frame if you cannot get yours working too

x2...If the screws do not seat the lens properly you will not get a connection. My local dealer offered to replace them for free.

But after I blew both of my LP lamps, I replaced them with these:

These things are super bright and actually make the LP lights look waaaay better than the stockers. Also no error codes. Just a straight swap with resisters built in. Bought online received it fast and with no problems. They were about $40 bucks with a $7 shipping charge. So if you're willing to jack $50 bucks for some LP lamps then they work great. Plus LEDs typically last longer than regular bulbs IMO...I could be wrong.

Clicky Click

**amuletA4** · 03-05-2011 04:48 PM

Yeah, the lenses are nice and firmly seated. The screws are exactly the same. I did happen to replace the bulbs with some LED festoon style bulbs that I got off e-bay because I didn't really feel like forking over $50 for a stinking license plate light. I tested the LED ones I got with 12 volts and they work nice, pretty good deal at $10 for 2 bulbs.

**GeoergeA402** · 03-05-2011 04:55 PM

I just went to local auto store and bought two for like $7 bucks and they work just fine!!!

**EBG 18T** · 03-06-2011 05:32 AM

It seems as though the led bulbs are hit or miss in the licence plate lights. Everything inside the holder has to be 'just right' for em to work 100% of the time. I ended up going back to regular bulbs as I was sick of the hassle from the led's.

**diagnosticator** · 03-06-2011 06:00 AM

The new license lamp holder screws should be Stainless Steel, or the corrosion and seizing of the screws will happen again. I have metric 3mm X 10mm long socket head screws that use a hex driver. Not going to deal with stripped screw heads ever again for the license lights.

OP, if you hear hissing before the power to the lamp fails, that is evidence the circuit is wet and is shorting out. After the lamp goes out, first, turn off the lights, and with the ignition key removed from the ignition switch, and the fuse removed, use your DVM on Ohms Auto Range, (If the meter has that, otherwise use the higher range scale and drop the scale range as needed for best resolution.) and measure the resistance from the lamp socket +DC terminal for the lamp, to chassis ground. With the license plate lights removed you need to measure between the lamp holder power contact and chassis ground. There must be infinite high resistance, aka, an Open Circuit, between the lamp power +DC terminal and chassis ground. (Most meters display an over range character instead of numbers when the resistance is higher than the range scale maximum.) Anything lower, is a short to ground. From your description of the symptoms, it is a practical certainty the circuit is shorting out, obviously, this must be fixed.

**diagnosticator** · 03-06-2011 06:15 AM

Originally Posted by sa_seahawker

x2...If the screws do not seat the lens properly you will not get a connection. My local dealer offered to replace them for free.

But after I blew both of my LP lamps, I replaced them with these:

These things are super bright and actually make the LP lights look waaaay better than the stockers. Also no error codes. Just a straight swap with resisters built in. Bought online received it fast and with no problems. They were about $40 bucks with a $7 shipping charge. So if you're willing to jack $50 bucks for some LP lamps then they work great. Plus LEDs typically last longer than regular bulbs IMO...I could be wrong.

Clicky Click

Nice design on those LED lamps. I think almost all LED license plate lights are way to bright however. I mean, c'mon, the license plate light is only supposed to be just bright enough to make the license plate visible, not light up the entire rear bumper and the road behind the car 10 feet wide and 6 feet back as well. I have most of my lenses covered with aluminum tape as a quick fix, but I am planning on adding a resister to the power supply to the LED to dim the brightness a lot, instead of the white trash tape-over I'm using now.

**audimontreal** · 03-06-2011 10:59 AM

Originally Posted by diagnosticator

the license plate light is only supposed to be just bright enough to make the license plate visible, not light up the entire rear bumper and the road behind the car 10 feet wide and 6 feet back .

Amen to that. I am sure that some members even wondered if they were able to put an HID kit as well!

ECS sells nice ones for $50 but you can get cheaper as long as they have built i resistors...

**amuletA4** · 03-07-2011 04:29 PM

Originally Posted by diagnosticator

The new license lamp holder screws should be Stainless Steel, or the corrosion and seizing of the screws will happen again. I have metric 3mm X 10mm long socket head screws that use a hex driver. Not going to deal with stripped screw heads ever again for the license lights.

OP, if you hear hissing before the power to the lamp fails, that is evidence the circuit is wet and is shorting out. After the lamp goes out, first, turn off the lights, and with the ignition key removed from the ignition switch, and the fuse removed, use your DVM on Ohms Auto Range, (If the meter has that, otherwise use the higher range scale and drop the scale range as needed for best resolution.) and measure the resistance from the lamp socket +DC terminal for the lamp, to chassis ground. With the license plate lights removed you need to measure between the lamp holder power contact and chassis ground. There must be infinite high resistance, aka, an Open Circuit, between the lamp power +DC terminal and chassis ground. (Most meters display an over range character instead of numbers when the resistance is higher than the range scale maximum.) Anything lower, is a short to ground. From your description of the symptoms, it is a practical certainty the circuit is shorting out, obviously, this must be fixed.

@diagnosticator- Thanks for the tips, I'll have to take a closer look. What part of the circuit is most likely to be wet; an assembly in the trunk lid or elsewhere in the vehicle? Also, you mention a fuse...where is this fuse located and is it for all the exterior lights?

**amuletA4** · 03-07-2011 04:33 PM

Originally Posted by audimontreal

Amen to that. I am sure that some members even wondered if they were able to put an HID kit as well!

ECS sells nice ones for $50 but you can get cheaper as long as they have built i resistors...

Yeah, I totally agree. I really like the LEDs I got- they only have two LEDs per bulb, have a heat-sink, and resistor built in. Now if only I could get my circuitry working...

**Grantola** · 03-28-2011 02:24 PM

Hey Jake,

I've just had exactly the same problem with my B6 A4 Avant over here in Scotland, strange fizzing sound from the tail door, license plate lamps going out despite the bulbs checking out ok. I've root caused the problem and just wanted to let you know what I found.

I'm not sure whether the parts are shared between the Avant and the sedan, but it seems like there's a weakness with the moulding which carries both the touch pad for the tail door release and the two license plate lamps. It's basically a two-part strip with the mechancial mounts for the two license plate lamp mouldings at either end and the touch pad in the centre. There's a second moulding which clips into the first, the second moulding contains the microswitch for the boot release, the (moulded-in) wiring for the two license plate lamps and a 4-way connector for the electrical connection to the tail door harness.

What I found is that the moulded-in wiring had been arcing at a 90 degree bend in the wire, opening the seal/moulding and as a result one of the license plate lamps had gone open circuit.

Perhaps coincidental, but I've had a problem with the rear wiper motor leaking the water for the rear window spray into the tail door (turns out that the B6 Avant has a fundamental design flaw with wiper motors, the rotation of the wiper shaft wears the water seal, water leaks into the motor gearbox, eventually destroying it). The water had been running down over the area where the licence plate lamp connection failed, probably unrelated because the arcing has come from the inside and eventually opened the moulding, which has then probably not been helped by the water once the wires have been exposed.

I've replaced the moulding (both parts come as a complete unit under part number 8E0 827 574 C (that's the Avant part, might be different on the sedan)) and the problem is fixed. £45 plus tax which I guess is around $70 plus tax in the US.

There are four nuts (two semi-captive) which have to come out to get the moulding out, it's a bit awkward to get access, but I figure it's about a 30 minute job if you're handy with a spanner. Biggest problem I found was getting the tail door trim off, the clips are hard work.

Once you're in there you might might as well replace the latch solenoid as well (4B9 962 115 C). £30 plus tax, again around $45 plus tax in the US. Seems to be another common problem, the latch makes the release noise but doesn't open the tail door. Mine got worse and worse until it would only open about one time in 10.

Interestingly, both parts were in stock at my local parts shop, usually a good indication that they sell loads of them and that normally indicates a common problem!

Hope that helps!

Cheers,
Grant

**jackyaudi** · 03-28-2011 02:43 PM

Originally Posted by EBG 18T

It seems as though the led bulbs are hit or miss in the licence plate lights. Everything inside the holder has to be 'just right' for em to work 100% of the time. I ended up going back to regular bulbs as I was sick of the hassle from the led's.

Well so far from experience it seems not all A4s react exactly the same as far as the License plate LEDs go. Some cars I just slap them in with 0 other work and they just run fine even after a while. Other A4s, like mine, I would had to adjust the connectors, clean the contacts, make sure everything is nice and clean, then make sure the housing is fully in and the screws all the way in before the thing works fine.. It took about half an hour of messing around with it. so its some work to get it right, but once done, its fine. I had mine for more than a year now without issues. It also depends how hard people slam their trunk doors over time I noticed.

**michgo** · 03-28-2011 02:45 PM

Originally Posted by Grantola

Once you're in there you might might as well replace the latch solenoid as well (4B9 962 115 C). £30 plus tax, again around $45 plus tax in the US. Seems to be another common problem, the latch makes the release noise but doesn't open the tail door. Mine got worse and worse until it would only open about one time in 10.

Hope that helps!

Cheers,
Grant

Truth has been spoken. Please if you go through with the labor, replace this

**jackyaudi** · 03-28-2011 02:50 PM

Originally Posted by diagnosticator

Nice design on those LED lamps. I think almost all LED license plate lights are way to bright however. I mean, c'mon, the license plate light is only supposed to be just bright enough to make the license plate visible, not light up the entire rear bumper and the road behind the car 10 feet wide and 6 feet back as well. I have most of my lenses covered with aluminum tape as a quick fix, but I am planning on adding a resister to the power supply to the LED to dim the brightness a lot, instead of the white trash tape-over I'm using now.

Please do let me know how that goes, usually the resistors are sometimes added to avoid the license plate errors on some models, but I would be interested to know if it helps brightness levels to something that lightens just the license plate as in your case.

Sometimes I do like the extra brightness when the car is dirty and covered up with dust/mud/dirt/etc, other times I feel when car is clean its beyond what the plates need. Same thing goes for HIDs I guess, most of them are too bright, even the factory ones from Audi for the headlights, but I guess people like them coz they look "cool".

**1NaudiA4** · 03-28-2011 10:14 PM

As for the LED license plate lights being too bright it also matters what color the car is. The LED's on a silver car will appear much brighter than a black or red.

These are the ones my buddies with B6's and B7's run; LED License Plate Light from Super Discount LEDS. No errors except for some of the B7's

**FoRbAnNa** · 03-29-2011 06:50 AM

Originally Posted by jackyaudi

Please do let me know how that goes, usually the resistors are sometimes added to avoid the license plate errors on some models, but I would be interested to know if it helps brightness levels to something that lightens just the license plate as in your case.

Resistors in this case can serve two different purposes, If the resistor is in parallel with the LED(s) it can trick the board computer to not throw a bulb out warning for the licenseplate lights. But if the resistor is in series with the load (read LEDs) you can dim the lights with a simple resistor. Where different resistor values leads to different light outputs, just like diagnosticator talked about.

**jackyaudi** · 03-29-2011 07:20 AM

There is actually 2 much simpler solutions:

1. Adjust the LED to face more towards the opposite direction of the housing therefore decreasing the light output. If needed a little soldering will keep it exactly in place, takes 2 minutes to do.
2. The problem is that the angle of the license plate housing points the lights towards to bumper and the street afterwards. If for example you would cover the first 30% the license plate housing (either from inside or outside), it would actually just light the plates and nothing else.

With the above ways you can keep the brightness as is or decrease naturally it by turning the LED inside around.

**iamshayan** · 03-29-2011 08:09 AM

lol when I did mine, first the screw head broke off, so i had to drill it out, then one of the plastic light coverss were covered in orange juices from rust, the insides were corroded with white calcuim to the point where neither of the bulbs would make a connection.
I bought new plastic covers from the dealeership and bulbs from jackyaudi,
ended up removing the whole handle mechanism thing from the inside of the trunk, sanding it all down and paintig it black again, because the whole peice looked like ass and didnt work for shit.
i admit, it was alot of work just to make the plates light up for cops to give me tickets

**jackyaudi** · 03-29-2011 08:17 AM

You can also get a ticket for having no license plate lights in the dark.

**iamshayan** · 03-29-2011 09:04 AM

Originally Posted by jackyaudi

You can also get a ticket for having no license plate lights in the dark.

& i dont need any more of those!
this is why i did it.

**ceeteesnowboard** · 03-29-2011 07:16 PM

i might just go with the new led's. my error code has gone on, checked it out and the metal brackets that hold the bulbs are just shot.

**CoreyRS** · 04-27-2011 08:16 PM

bump

any idea how to fix the short (when you hear hissing)?

**Grantola** · 05-01-2011 12:46 PM

Hey CoreyRS,

You can't repair the unit mate. The wires which are shorting are encased in some sort of plastic/silicon goop and the whole assembly is a moulded unit. You'll need the complete assembly. I'm (a) Scottish (infamously, the most tight/Scrooge-tastic race on the face of the Earth) and (b) a pro electronic engineer, so you can trust me when I say I'd have rather fixed it than replaced it. As far as I can see there ain't no easy way to fix it!

The part you need is 8E0 827 574 C (that's the Avant part, might be different on the sedan, check it).

Cheers,
Grant

**CoreyRS** · 05-19-2011 03:06 PM

if anyone is still having problems with the hissing...I have an extra harness for sale in the classifieds for $75 shipped.

**amuletA4** · 07-30-2011 09:41 PM

Grant- thanks for the info! Now that the rain has stopped I haven't been caring too much, LOL. However, I know this still needs to get fixed, sounds like a good little summer project replacing the moulding.

Corey- the harness you mention for sale, is this the moulding part that Grant described as being the culprit of the problem and is it for a sedan or avant?

Respectfully,
- Jake

**CoreyRS** · 07-31-2011 02:52 PM

Originally Posted by amuletA4

Grant- thanks for the info! Now that the rain has stopped I haven't been caring too much, LOL. However, I know this still needs to get fixed, sounds like a good little summer project replacing the moulding.

Corey- the harness you mention for sale, is this the moulding part that Grant described as being the culprit of the problem and is it for a sedan or avant?

Respectfully,
- Jake

I am not sure if the harness/molding will work for an avant, but I can check. It does fit a sedan though. I bought the harness, and then realized that my OEM harness was just fine :-(

**amuletA4** · 07-31-2011 04:51 PM

Oh good to know... I have a sedan, so no worries checking on whether it works for an avant. Do you happen to have a pic of it? Also, if it wasn't your harness causing the problem, what did it end up being?

**CoreyRS** · 07-31-2011 09:50 PM

**jayiszraw** · 07-31-2011 10:16 PM

Originally Posted by CoreyRS

just confirm, is that harness and bulb holder 1 piece?

**IndianDrives** · 07-31-2011 10:44 PM

It seems that the LED lights are hit or miss the plate. All inside the holder is right for em to work 100% of the time. I ended up returning to normal light bulbs because I was tired of the hassle of the LED.

**CoreyRS** · 08-01-2011 10:14 PM

Originally Posted by jayiszraw

just confirm, is that harness and bulb holder 1 piece?

the bulb holder is attached to the clear plastic covers you can see above your license plate. The harness replaces the wiring, molding, and contact pads that the holders press against. Does that makes sense?

**amuletA4** · 08-02-2011 11:39 AM

Originally Posted by CoreyRS

I am not sure if the harness/molding will work for an avant, but I can check. It does fit a sedan though. I bought the harness, and then realized that my OEM harness was just fine :-(

@CoreyRS, did you get the hissing problem fixed?

If so, what did it end up being since your harness was fine?

**CoreyRS** · 08-03-2011 08:36 AM

Originally Posted by amuletA4

@CoreyRS, did you get the hissing problem fixed?

If so, what did it end up being since your harness was fine?

I am not exactly sure what the hissing was caused by, but when I took apart my trunk so that I could see everything, I tried the stock bulbs again. They worked just fine (the hadn't worked for over a year)...so I tried the LED bulbs and they worked as well. The only thing that I changed was cleaning the contact pads that the bulb holder presses against ( which is at the end of the harness I have for sale), but they didn't look dirty or corroded to begin with so who knows.

**amuletA4** · 10-01-2011 07:29 PM

Thanks to all of you for your help and insight, I was able to get my malfunctioning license plate lights back to working properly!

Root Cause: Lights were non-functional due to break/short in wiring harness

Solution: Replace wiring harness (P/N 8E0-971-145, bought mine from CoreyRS-thanks bud!)

For your entertainment, here are the steps I took...

1. Remove warning triangle- twist knob
2. Remove holder for warning triangle- depress lower two tabs to pop off holder

3. Remove single screw (Phillips) next to interior trunk closing handle

4. Remove plastic cover on trunk latch mechanism- pull firmly straight away
5. Pop-off glow-in-the-dark cover on trunk safety release handle

6. Remove remaining trunk safety handle (#25 torx)
7. Remove trunk lid carpeting- carefully pop eight clips away from metal trunk lid

8. Remove four nuts (10 mm) along backside of license light/exterior soft handle assembly
9. Disconnect wiring harnesses
10. Disconnect lock release cable from key-lock mechanism- both metal end and plastic fitting

11. Remove key-lock mounting bolt (10 mm, mine was greenish in color)

12. Twist key-lock mechanism approximately ¼ turn clockwise and pull backwards to remove from light/soft handle assembly
13. Remove license plate mount- (~#25 torx and adhesive) *This is possibly optional, however I found it nice to have the extra room to pull the assembly out in the next step*
14. While pulling light/soft handle assembly out, depress plastic tabs on top of the light housings otherwise the assembly will not come out
15. Remove two screws (#25 torx) from back side of soft handle on light/handle assembly

16. Clean assembly and replace (or repair if possible) wiring harness (PN 8E0-971-145) for license plate lights and exterior soft handle-** I happened to find some corrosion on my assembly and after cleaning, I ran a bead of silicone along the OEM weather-strip to add some extra protection against future water infiltration
17. Return everything back to its place following the guidance in the above steps and success shall be yours!

Cheers!

- Jake

**CoreyRS** · 10-01-2011 08:55 PM

nice write-up...much better than I gave you! haha, glad I could help though.

**Joey0918** · 01-11-2012 05:38 PM

3 months mine has been out and havent been pulled over yet

**amuletA4** · 01-11-2012 08:54 PM

Nice! That's about as long as I went without them working. It wasn't too much of concern of mine, but I figured that with the hours that I work, I would mostly be driving in the dark this winter, making my chances of getting pulled over somewhat increased.

And since I fixed my lic plate light, I have had the pleasure of dealing with two other electrical related problems

1) Replaced my radiator fan relay (# 219) after the fan kept running and drained my battery - relay was fried and had a bit of water in the box under my ECU
2) My left front turn signal stopped working - bulb wasn't bad, but the connections on the bulb housing we not making contact

Must be all this excessive Pacific NW moisture...

All in all, I'm sure that fixing all this crap my self saved me mucho!

**subversion** · 04-22-2012 09:58 AM

After taking apart the bulb housing, I can no longer put my key into the trunk lock. Has anyone else run into this issue? I made sure, twice, that everything was connected properly. I've waited 2 weeks to see if the issue would resolve itself, but it hasn't. I'd appreciate any help. The trunk itself has no trouble opening, if I open it from the outside with the button it unlocks just fine, it's just that the key cylinder won't slide over to allow me to put the key in.