I have a 2001 (new shape) A4 saloon, which I have fitted an aftermarket head unit into. Unfortunately the wiring loom doesn't seem to provide a
12V switched ignition feed to turn the head unit on (the factory unit I believe used CAN-bus), with the result that I have to manually shut it down when I leave the car.
Is there anywhere that I can easily get a 12V switched feed from?
Also this particular head unit takes some time to power up, is there an alternative location I can take a permanent 12V feed from so it doesn't turn off when starting the engine? (Preferably without having to run an extra cable to the battery or anything silly like that...)
Audis and VW's traditionally reverse switched power and permanent on (yellow and red I believe) in the ISO connectors at the back of the radios. so you might need an adapter or you might need to reverse those cables in the connector.
Careful! This was certainly true on older cars, but the more recent Audis do, as Glenn suggests, only have a permanent live to the radio and use CAN bus signals for the power up/down commands. This change occurred, I believe, when the Concert II/Symphony II range of radios was introduced. Without referring to the workshop manuals, I wouldn't be certain as to what to expect on a 2001 B6 A4, but suspect that it will use CAN bus control.
On my car (a 2003 RS6), I found a row of relays behind the panel below the steering wheel, with threaded studs to which you can easily add additional connections. One of these has a switched output, the rest seem to be permanent live.
There's no wire going into the ISO plug for the switched live feed, so it definitely uses CAN-bus. It had the Concert II head unit (single CD player) fitted when I got it. I've had to join the red and yellow wires together and attach them to the permanent 12v feed on the ISO plug.
My previous car (a 1999 A3) had a Chorus radio-cassette with separate
6-disc CD changer, and did have the switched feed on the ISO plug, but it was a little unreliable - I think this may have used CAN-bus. When I fitted my Sony kit in there I had to modify the adaptor harness a little.
You have an RS6? You jammy git! I want to drive it! :-P
A bit of prodding with a multimeter has revealed a 12v ignition switched feed on fuseway 5, which is the one for the factory phone hands-free kit. As I have a Bluetooth kit taking its power from the ISO connector on the head unit I don't think drawing a tiny switching current off this will be a problem. :-) (The Bluetooth kit runs through a line-level adaptor that switches the front speakers over to telephone when a call comes in, with the head unit muting the rears and sub.)
I'm holding off doing this for the time being though, as my new head unit (Sony MEX-1HD) requires that I rip all my CDs onto its internal hard drive. So for the last few days I've been leaving the car on the drive with the head unit powered up, going out every few minutes and changing the CD over. What I'm considering doing now is taking both a permanent and switched 12v feed to a toggle switch mounted behind the fuse panel so I can have the option of running the audio without the key in the ignition, but normally leave it on ignition switched mode. That way the music starts and my Bluetooth kit connects automatically.
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