Hey all i'm Rok from Slovenia and i'm new on arduino

My question is:

How can i control a car throught arduino? Like:

Lock/Unlock car, Open/Close window, Turn on/off lights... ?

I know that arduino output voltage is 5v and the car voltage is 12v ? so do i need any amplifier or ?

Thanks for any help..

There are 2 ways of doing this, each have their own good and bad points.. Not knowing what you want to do, or what you have for a vehicle, or your abilities I cannot make a recommendation..

1) for each circuit you want to control you will need to cut into the circuit and possibly/probably disconnect the circuit temporarily from the rest of the vehicle.. ex:power windows, lots of manufacturers pull both leads to the motor to ground.. When you want to move the window they remove ground on one circuit and provide power, thereby moving the window.. The other side is still tried to ground.. If you were to simply try providing 12v power thru a relay without first disconnecting that circuit from the vehicle you would be causing a short since it is still tied to ground.. In essence you will need to research each circuit you wish to control, find out how they do it and come up with a plan of attack that will work for each..

2) depending on your vehicle, and how new it is you may be able to do it with data line communications.. My vehicles are either class 2 vpw or high speed CAN, or single wire canbus.. Yours will be different I'm sure and you might not have the capability that mine have.. I can turn the nav radio backup screen on with a command, I can roll down the windows, I can honk the horn, turn on parking lamps, control door locks, etc.. all with commands.. The problem with this is that the other modules will still send out commands on their own, sometimes conflicting with my own.. But for simple parking lamp control, door locks, horn honks, etc, you should be all set.. It starts getting interesting when your trying to tell the radio it's in reverse so the camera turns on when in the next message the BCM is stating that it is in park, they conflict and the radio goes nuts trying to make everybody happy.. For something like that you need to do a 'man in the middle attack' which reads and forwards messages as required to keep the radio running,steering wheel controls working, etc while intercepting the messages you don't want forwarded..

good luck, you'll need lots of research before you decide which way to go..