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.
Peter Bell (Note Spamtrap - To reply, replace 'invalid' with 'bellfamily')
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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