2007 A4 B7 no power to radio - please help me

[xionis]

I have been searching all over google for an answer, i've read many threads similar to my problem but no one had an answer that helped me. Most said check the fuses, which I have done and even replaced them with new ones. First I will post my detailed story, and at the end I will try to give a brief summary of it for those who don't want to read my novel. I just want to provide as much info as possible in hopes that it may help to resolve the issue.

Long detailed version:
First I was going to attempt to change out my HID bulbs following a tutorial I found on here to "easily" replace them without removing the bumper, I followed the instructions slowly and carefully as I didn't want to damage any bulbs....but I never even got that far. The first step said to disconnect the battery, so I did the next step was to move the reservoir behind the driver headlight out of the way to gain access to the opening so I could remove the bulb. So I tried, I couldn't gain more than 2in of clearance.....I studied the images he posted and my setup, they looked the same but apparently I lacked whatever magical power he possessed because there was no way it looked possible for mine. After an hour I gave up and mounted the reservoir back (this was the only thing I unscrewed).
Next I reconnected my battery, and noticed my stereo didn't come on, my ESC light was on and that my buttons on my keyfob nidn't work. I found on a forum to hold the unlock button with the key in to reprogram it....so I did, now the buttons work again and the ESC went off, but my stereo still did not power on or illuminate. I checked the fuse at the driver side door and it was fine but I replaced it anyway with the same amp rating. Still nothing.

I took it to my mechanic because I was due for my timing belt change anyway and asked him to look at my radio as well, since he works on a lot of Audi's he assured me that he knew what the problem was right away, that it needs a secret code because I disconnected the battery. I was relieved but when I picked it up the next day he tells me that he checked the system and that the radio just wasn't getting power and that it was just dead and needed to be replaced. So I replaced it last week, everything went smooth and it powered on right away. I think it was Tuesday (3-4 days after install) I was leaving work and my music was playing just fine for about 3min. then shut off, It was a 90+ degree day so I assumed it overheated since my car was sitting in the sun all day and I have no tint on my windows. I blasted the A/C the whole way home in hopes it would cool off and turn back on. During my 30min. drive home it never came back on. I even pulled over to turn the car off/on again midway through my way home, but still nothing.

After letting my car sit for about 4 hours I went back out to see if I could fix the issue, I checked to see if it would come on first but nothing. Then I started checking things 1 by 1 and turning the car on each time to see if I could narrow down the issue. I checked all fuses and they were fine, I checked the wiring and everything seemed tight and the main harness was locked in. I disconnected my main harness anyway and plugged it back in, I turned the car on and once again my radio was working until today (2 days later)

So tonight I once again checked all the fuses and assumed I would just need to unplug the main harness again and then plug it back in, I did that as well as making sure all other cables were well connected. Nothing this time, so I got out my test light. I checked the fuse box at the door and I had power, I went to the main harness from the car and I had power from the 2 green wires and a brown one I think kinda had a flicker (it was on the 2nd row is all I remember) I plugged in my new stereo and checked the other end of the harness that plugs into the stereo itself, and I was still getting power from the green ones. However the stereo still wouldn't power up. Next I thought to remove the negative terminal once again since that was when this all started, maybe something will happen. So I removed it and allowed it to set for about 10min. while I was waiting I decided to clean the battery post as well as the connector on the cable using a wire brush battery terminal cleaner. While I was doing so I noticed that it appears that I have the original battery, which means it would be 9 years old now. It looks like there was a VW/Audi manual or booklet stuck on the front of it but I couldn't get to it without pulling the battery out. I noticed the was a small round window and the sticker on the battery said if it's black it's good and clear it needed replaced. From what I could tell it looked clear, but I have never seen one that was black so i'm not sure if they meant solid black because I could see into mine, and it looked to have black at the very bottom (about 1in. down) of the window.

So since everything seems to get power, my only theory is could it be that it's just not getting enough? How would I be able to measure if my battery is good or not? I would assume my car wouldn't start if my battery was bad. It also strikes me as odd that this all started once I disconnected my battery for an hour and I had no issues before then.

Sorry that was so long....now my attempt to write a summary that isn't as long but still detailed for the most part...
Short version:
1. disconnected battery for 1 hour
2. stereo would not come on. mechanic looked at it and said stereo was dead.
3. bought new stereo and installed it. everything worked fine for 4 days. Then new stereo turned off on my way home.
4. later that night all fuses checked out ok, disconnected all harnesses and reconnected and new stereo came back on.
5. 2 days later new stereo went off again. repeated steps in number 4, new stereo still won't come on,
6. checked fuses and wiring with test light and power was going through the green wires all the way to the stereo.
7. disconnected battery for 10min. and cleaned terminals of battery. new stereo still won't turn on.
8. Noticed the battery appears to be the original, which means it would be 9 years old.
9. wondering if the old battery could be the problem even though the old stereo worked fine before the first time the battery was disconnected. How should I test? Would this cause it?

Details on my car:
2007 Audi A4 Premium
I do NOT have Bose system
I had the Symphony II stereo originally


Thank you kindly for reading my post and I would greatly appreciate any suggestions anyone has, i'm sure there has to be a few things I haven't tried. I am out of ideas though.

[SlvrAvnt3.0]

Check the ground. Make sure there's nothing funny going on with it.

[xionis]

Can't believe I didn't think of that....but still no luck. I checked the battery today (engine off) with my multimeter and i'm getting a solid 12.8v, i checked the ground and power going to the stereo and it is showing a steady 12v as well. I removed the fuse from the back of the stereo and it's showing 12v as well. Now i'm really lost. Power is going through but 2 stereos now won't come on all because I removed the negative battery cable for an hour.

Other than the power, is there something else that controls when/if the stereo comes on? Something like a wire that detects if the car is on? That's all I can think of now after testing the power and ground, unless someone else has other ideas.
If anyone knows location or color of any wire that may tell the stereo to come on please let me know so I can check that next.

Thanks in advance!

[SlvrAvnt3.0]

Did you run a separate accessory wire from an ignition source? or did you connect both constant and accessory wires to the same point?

[xionis]

I used a plug and play harness that is pre-wired for the A4.

Yesterday I disconnected the battery again and left it sitting for 6 hours. Then checked every fuse in the fuse box as well as the fuses on the back of both HU, I checked all the wires once again and decided to try the old stereo again, still nothing.... Then the new one, still nothing.

I'm only assuming that the wire harness I got for the new one is fine because it worked for 4 days which leads me to believe the issue has to be somewhere from the battery to the end of the harness since it has affected both HU.

After I had disconnected that battery that started this whole issue I tried for a week to get it back on, but once I plugged the new one it was fine for a few days.

This is a stupid thought I had, but I know some stereo have a security feature that won't allow them to work until you put in a code. Since the new stereo also stopped working days later is there an general code that would affect any stereo that is plugged in? I would imagine it being a sequence using the key fob and possibly steering wheel controls. But as I said... Dumb thought while trying to figure out this mystery.

I did notice one strange thing last night but i'm not sure if it was a bad connection or not... But this may help, I tested the jack for the radio fuse and it measured about 6v, and SLOWLY began to increase.... Approx 45-60 seconds it went to 8v. But when testing the power wire to the stereo it's measuring 12.4v, and when measuring the stereo fuse jack when it's plugged in it reads 12.4. I'm pretty sure the leads were making good contact with the fuse box, but would that low voltage be normal?

Sent from my Samsung Galaxy s7 edge

[xionis]

Lastnight i decided to connect my noco genius charger to the battery, which indicated that my battery power was around 75% so I allowed it to charge to 100% then allowed it to set for a couple of hours and checked it again and it showed that I was still at 100%. However the stereo still wouldn't turn on.

I made sure I had a good connection to the leads in the fuse box for the radio and my multimeter and it is definitely showing 6v and slowly starts to increase. I'm wondering if this should be higher.

Sent from my Samsung Galaxy s7 edge

[Christian@enfig]

Check the power and ground wires on the back of the radio. If they are getting power and ground then check the fuse on the radio for corrosion. It does sound like you just got another bad radio.

And this is exactly why I don't recommend people disconnect the battery when they do simple work on their car.

[xionis]

Tonight I took out the new stereo so I could ship it back, since I didn't want to look like I was the victim of a break in I put my old stereo back in instead of having an empty hole. I had the car off, and for some reason I decided to plug the harness in even though I just tried this stereo 2 days ago. As soon as I plugged it in, I heard the cd changer making sounds....so i turned the car on, and there it was....my original head unit started playing music right away. I turned the car on and off a few times in disbelief, and its still working....but the new one isn't.

As I posted recently, the only thing different I did since the last time that I plugged in the old one was that I charged my battery, since my Noco Genius charger said my battery was at <75% ........So if anyone else is having this issue try that, but for some reason I have a feeling that this story isn't quite over.....I think it's only a matter of time before my car becomes possessed by music hating demons again