I have bought the Start Engine Stop Button 8U0 905 217 A, can somebody please help me how to install it, to conect it so when i put the key in the contact i can push the button to start the car, if it is possible something like this.
I'm afraid this fitment is much more complicated than merely buying the button. This function is also associated with Advanced Key, which it sounds like you don't have. That means at least another control module, new keys and some additional coding to integrate the keys into the Central Electronic module as well as the alarm module and advanced key module. I do not know the sequence or details to do this as all NAR cars already have Advanced Key as standard. Someone from the RoW who has tried this or knows how to, will have to step up to help...
I know exactly what it means to activate the keyless function. But i do not want that function, i only want to install the Start / Engine / Stop button. I belive if i put the key in the ignition and turn it on when i push the button the car motor will start, and i want to iluminate the button only for decor. That is what i want to install if it is possible.
Okay for just that purpose, I have no idea whether you could certainly make it work, but I'd guess it's possible. As far as I know THAT function NOT available on the Q3. Some Audi models, the last Q7, a few older A4s had a similar set up, but they too had Advanced Key already built in in addition to a 'normal' ignition switch where the same key could be used either way. I have not seen a Q3 with both a conventional ignition switch AND a button, so I am not much help with this mod. I believe you could somewhat easily parallel wire the button with the ignition switch start contacts, but that's a bit of wiring work for you, without existing wiring parts to accommodate. And I doubt you'd be able to shut the engine down this way - that requires more integration with the Advanced Key module. The lighting requirement wouldn't be too hard either, another couple wires/connections... If you figure it out and do it, let us know - sounds cool.
You are right, if i want the button to work, i must adapt it to the normal ignition and that will be very hard but not imposible . I installed today the button just for decor, i wired it to illuminate and everything looks great