Re: Stereo installation

[steveb@newkla.kla.com (Steven Buchholz)]

The extra battery line probably powers the memory of the radio.  All of 
the Audis I've owned supply power to the stereo at all times (not just 
when the ignition is turned on), and it is up to the radio to ensure that 
the current drawn does not end up draining the battery after being left 
alone for a while.  As long as there are no pilot lights that come on 
when the "power" terminal is activated you should be able to wire the 
power and battery wires together and connect them to the Audi wire that 
is not brown.  I'd recommend hanging an ammeter in series with the "power" 
line when the radio is turned off to find out what the off current is.  
If it is less than 20mA then you are probably OK.  If you see a reading 
of 100mA or above you are asking for trouble.  The easiest solution would 
be to find some existing circuit on a load reduction relay that can handle 
the extra load.  Me, being an electrical engineer and NEVER doing things 
the easy way ... I wired up a quickie circuit with a separate relay to 
switch the line going to the "power" connection on and off using the 
switch that activates the buzzer when there is a key in the ignition to 
enable the main power when a key is installed in the ignition switch.  
I do like my implementation.  

RECAP ... (since I carried on a bit)
1) Yes the "battery" connection is meant to be connected to the positive 
terminal of the battery, and if you check you should find that the wire 
supplied by Audi does exactly this.  

2) Be careful connecting the "power" terminal to the Audi wire.  It should 
work with no problems as long as the off current on the "power" connection 
is not too high.

3) There should be no concerns about wiring directly to the battery as 
long as you do a careful wiring job, the line is fused.  If your battery 
is under the seat, make sure the rear seat isn't smashing the wires or 
the fuse holder!

4) The separate battery line should actually have a very low current draw, 
and is used to power volatile memory circuits that store radio channels 
and such.

5) Since Audi is different than most anybody else your questions really 
were Audi related!

Steve Buchholz
s_buchho@kla.com