OEM rear light issue - very bizarre - help/input appreciated!

**Wanted** · 05-14-2008 02:45 PM

2003 B6 3.0 Quattro
OEM rear lights

I've searched every conceivable rear light issue config to no avail however I did find one that suggested swapping all bulbs for new so I did that and here I am.

Oddest thing going on with the rear lights and I'll do my best to lay it out clearly.

Friday of last week - turn the car on and get a "left rear light" out message before heading out of town for the weekend. Stop and pick up a bulb from Autozone and it was a "lighting tech" bulb number 7506. Replace the bulb in the parking lot (doesn't look bad). Message light doesn't go out. Hmmm.

Drop wife and daughter off at hotel a couple hours away and go to another AZ I saw on the way in. Get another 7506 - match up the numbers to make sure I didn't monkey finger it. Replace bulb - reassemble. Start the car and message light doesn't go out.

Go home on Saturday evening. Match new bulb with old bulb. Same info. Disassemble both lights and switch all bulbs from left to right and vice versa. Reassemble - now the only thing that works is right blinker, rear fog and nothing else (brake light in rear window is fine). So the right which had no issues at all - now has most everything out when I put it back together.

Go to Pepboys pick up all new Sylvania bulbs for both lights - bend all contacts upwards a little, apply die electric grease (which i've never used before on bulbs in all my years) reassemble and same. Doesn't fix anything - no brake lights, left turn signal, hazards, running, etc.

Disassemble to the point the lense was removed but the harness was still plugged in, turn on lights - make note of the 3 out of 11 that work, turn car off, swap them for the other side, turn car back on and the same 3 worked in the same 3 locations with different bulbs!? So in essence a bulb that wasn't lit on the left side, now works on the right side WTH?

I checked the fuse (#14 and #31) and both are fine. What gives?

Any insight is appreciated!

**bavaria75** · 05-14-2008 03:17 PM

Very odd!!!
My input would be that your light bulbs seems to be ok. It might be in issue with the ground connection, as most of your bulbs on one side don't work.
Try the bulbs without reassmbleing, just leave the cover off and try again.
If not I suggest get the volt meter and ohm meter ready to control voltage on the socket and OHM out the light bulbs.

**FrostofSparta** · 05-14-2008 05:54 PM

I had a very similar issue with my Car. Brake lights would report burnt out but then when I restart the car and drive a little ways they would be back working. This happend the second day I owned the car. I was thinking it had Electrical problems. So I looked on Sylvania's Website and used their "light finder app" and narrowed it down to my car. I have an 03 A4 Quattro, it told me to use 7528 or 7528LL Sylvania bulbs. Ended up having the wrong bulbs in the brake sockets (Silly previous owner).... Now I haven't had a problem since.

**jessefrank** · 05-14-2008 06:57 PM

The only insight I can offer is to make sure the bulb contacts are clean and it's metal to metal (which it sounds like you have). I had an issue with the turn signals on my headlights randomly going out. I had to make sure all the contacts were clean, rebend them and replace the bulbs.

I'm going out on a limb here...but I don't think it's a bulb issus but kind of sounds like a wiring issue.
I'd check your harness for any visable cracks (I know my 02's wiring/connectors are pretty brittle due to age [i only have 57k on the clock]). Check the black plastic backing of the light (that the harness connects to and all the lights get power from) for any cracks hairline cracks.
I'm not sure where the wiring runs on our cars (from the front to rear), but if you can check that for cracks or damage.

...And not to be ruled out.....I had some very weird electrically tied issues when my Certral Locking Unit went bad in my car (everything from alarm issues, window controls, random interior lighting to headlighting). It may tie into the rear lights by the alram and door lock/unlocking...and it may be early signs of faliure.

If I think of anything else I'll let you know.
-Jesse

**old guy** · 05-14-2008 07:04 PM

I believe you are using the wrong bulb. Try a Sylvania 7528 and see if that fixes the problem. Clicky click

**a2gtinut** · 05-14-2008 07:19 PM

i hate those 7xxx numbers. Euro cars use only W5W, P21W, H11W,R5W, P21/5W etc

http://www.powerbulbs.com/product_cat.asp?cat1=39

**old guy** · 05-14-2008 07:36 PM

Unfortunately most of the car parts stores don't use those numbers. Here is a good cross reference for looking up bulbs: Clicky click The P21/5w 12v is the correct bulb (cross references to the 7528)

**KrUsTyX** · 05-14-2008 07:49 PM

Originally Posted by FrostofSparta

I had a very similar issue with my Car. Brake lights would report burnt out but then when I restart the car and drive a little ways they would be back working. This happend the second day I owned the car. I was thinking it had Electrical problems. So I looked on Sylvania's Website and used their "light finder app" and narrowed it down to my car. I have an 03 A4 Quattro, it told me to use 7528 or 7528LL Sylvania bulbs. Ended up having the wrong bulbs in the brake sockets (Silly previous owner).... Now I haven't had a problem since.

I have the same exact problem right now... this is

**Wanted** · 05-14-2008 10:39 PM

Man was this a fun one. All lights are working now - but not after a good fight.

I figured a good amount out about our cars and the diagnostic loop in different areas. It's amazing how zoned these rides are compared to my other two hobby cars where everything seems to be on a single "loop" (big jeep rockcrawler with lots of bolt on torque mods; Nissan Z 5 speed convertible with turbo conversion) the B6 is my daily. When I got home; with my 2.5 month old daughter running around the garage and driveway; I put my voltage tester to work and it was dead on consistant until I got to a bulb (sorry i don't know which socket) that dropped considerably. It was of the 7528 variety but was a "LL" (long life) and was a P21/5w 13.5V as opposed to a P/21/5W 12V. Aha!

I drove up to Napa and talked to the desk guy who let my daughter (who was being a CHAMP!) and I go back and compare EACH BULB with the correct one with corresponding V/W (according to - wait for it... an OLD GUY post)and pins and replaced all of the bulbs yet again just to be safe. AG (Anna-Grace) stood in the trunk and held the bolts while i dropped all the new bulbs in (I couldn't wait until I was home) and low and behold they all came back up!

It would seem that the spike in voltage really caused a drastic enough "bump" (although it doesn't seem to be much in these cars) to cause some deterioration in the loop. With that 1.5 strategically placed in the contact loop it really screwed things up (as OG or frostofsparta pointed out). I would say it was over a matter of 5 operating hours that it went from 1 light out (replaced with a Lighting Tech bulb) to 3 of the 11 working. I wish I would have paid enough attention to see if if the rest of the corresponding contacts/lights dimmed or glowed excessively such as they do when one in a christmas tree string goes out!

Thanks for all the input!

Now on to the damned sunroof spook switch. I've been in that thing 3 times already and I'm not ready to give up.....