A3: No Radio Power When Ignition Off?

Hello!
I'm having a problem with my A3 that I haven't been able to solve myself yet. Normally, the power to the radio only goes off when you remove the ignition key from the ignition. At least, that's how it was with my previous A3 and Golf 2. So, it should also be possible with my current A3, model year 2002. The problem is, I can't find this darn cable . I've already measured the main wires of the fuse box, but I can only find constant positive voltage or ignition positive voltage.
Does anyone know where I can find the necessary power source, or does anyone have a wiring diagram for the A3 that I can use to extract the information myself?
The standard ISO connector of the radio strangely only provides constant positive power . In order for me to get switched positive power, I already had to run a cable from the fuse box to the radio...

Sure, here is the translation of the text from German to English:

"MFG" is an abbreviation for "mit freundlichen Grüßen," which means "best regards" or "sincerely." It is commonly used in German-language emails and letters.

The ISO connector always has "ignition power," or rather, that positive voltage that's activated when the ignition key is turned. Is the ISO connector properly connected, or are the cables disconnected and lying somewhere inside the dashboard?

If the connector is present but not working, it could be a broken wire or an issue with the ignition switch. I'm not sure if this positive connection also goes through the fuse box.

http://www.selfmadehifi.de/kfz-iso.htm

I have a Blaupunkt Dallas MD70 in my A4 and initially had the exact same problem. The solution is to swap the constant power connection and the ignition connection (as far as I know, these are the first and third connections in the upper row).

But the most relevant link has already been posted above...

@mahk
I once experienced something similar. In that case, I realized it because the radio would work when connected, but the saved stations would disappear after turning off the ignition.

Well, the problem is that my ISO connector only has the following cables connected to it.
1. Long-lasting plus.
2. Mass.
3. Amplifier for electric antenna.

That's why I tapped into a switched positive wire directly from the fuse box and connected it to the radio. It's not the problem that the settings aren't saved; that all works perfectly. The issue is that when I turn off the engine, the power to the radio immediately cuts off. Normally, the radio only turns off when I remove the key from the ignition.
The ISO connector seems to be complete, as the protective casing starts immediately behind the connector and shows no signs of damage. Furthermore, the previous owner had already rerouted the switched positive wire away from the fuse box. In my previous 1999 A3, all of this was already included in the ISO connector, and the radio is the same model as well.

Okay, that's new to me. It worked on my A3. However, it didn't have an electric antenna, or are you talking about an antenna amplifier (I can't even remember, I thought it wasn't in the ISO connector)? In any case, that's where I would start and carefully check that connection again. What was missing in my car was the radio mute function (it also didn't have a hands-free system from the factory).

If you can't find what you're looking for, you absolutely need a wiring diagram that shows the location of the radio, fuse box, and ignition switch. Unfortunately, I can't provide that.

Disclaimer: No warranty.
Given the year your car was manufactured, the switching signals (radio on, lights, etc.) are likely already transmitted via CAN-Bus. However, these signals should then be present in the ISO connector. This should be solvable with a CAN-Bus adapter from the aftermarket.

My G3 is much older, so everything is without guarantee, but it might be worth looking into this direction.

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

guste100 wrote:

... Given the year your car was manufactured, the switching signals (radio on, lights, etc.) are likely already transmitted via CAN-Bus. ...

Basically correct, but then the car would need to have a FAKRA connector, like the G5.
http://www.golf5-sound.de/Quadlock.jpg
This connection has been in use at Audi since MJ02.

What kind of radio was originally installed in the vehicle?

Hi!
Thank you for the answers!
So, when I bought the car last year, there was no radio installed because the previous owner had already replaced the original one. Unfortunately, I don't know which radio was installed before, or whether an original Audi radio was ever fitted.
Okay, then I'll take a closer look at that part again and trace the cable a bit further.

Sure, here is the translation of the text from German to English:

"MFG" is an abbreviation for "mit freundlichen Grüßen," which means "best regards" or "sincerely." It is commonly used in German-language emails and letters.

On the B4 model, there's a 0.5mm² red wire at the control unit (KI) that has voltage as long as the key is in the ignition. It's possible that the wire color is the same on yours...