GPS Speedometer: Connect to Navigation?

Hello everyone,

A difficult question just before Christmas:

I want to install a navigation system in my Audi A4, manufactured in 2000, with the AJM engine.
Where can I get the speedometer signal (in the simplest possible way) for what's called 'coupled navigation'?

Thank you in advance.

Greetings.
Jürgen.

Are you looking for something here?
http://www.petri.de/cgi-bin/petri.cgi?kdnr=&val=0&un=00001044432697-3D75DAD4-00&usepic=../bilder/icon_suchen.gif&url=katalog.html&go=Montagehilfe%2fTachosignale

Great link!!

Thank you very much!

Greetings.
Jürgen.