S4 B5 Alarm output

[tdiquattro]

Does anyone know how to pick up the "alarm active" output on the B5 S4? I am thinking about an aftermarket sounder or cell phone transmitter and need to get a signal to tell it when the car is in alarm.

I know the ECU communicates with the sounder in the boot to tell it when to go off and also with the state of the doors, internal movement sensor, ignition, etc.

I may just take the sounder to bits and try to work out where the driver signal is for the noise.

Hope you can help thanks,

Nigel

[shineydave]

there's 3 wires going to the plug on the sounder, as far as i can see there's a live and an earth for charging the back up battery then a third wire that is the trigger, can't remember which way round they are but once you figure out the live and earth it's not eactly brain surgery to figure out which is the trigger, lol

[tdiquattro]

Thanks Dave, ill give that a try!

the only thing that confused me about that theory are the faults on Vagcom that state "communications lost with sounder etc.. which implies that is a 2 way data line or something, if it just goes to 12v on alarm thats easy, I will have a look.
Theres also an awful lot of circuitry inside the sounder box for just a tone generator.

Cheers
Nigel.

[shineydave]

the fault seems to be generated because the batteries provide the conduit to power the alarm (see petrol daves comments here http://www.rs246.com/index.php?name=PNp ... 1&start=15 )

if the batteries die then the link between the central locking controller and sounder is broken, the alarm can't respond as effectively there's no power there to run it. as to the question of whether it's a 2 way data line .........................errrrrrr