Hello guys , I own a grande punto 2007. The previous owner lost the key with the buttons and I want to install an aftermarket system. Is there anyone who has installed such a system to help me with the wiring? I made an attempt based on a tutorial I found here in the forum but no luck .

Why not ordering simply a new remotekey?
There are services hat offer that way cheaper than a Fiat dealer.
just an example is: theautolocksmith
Look for services/options/prices in your region, google is your friend.