Where do the other ends of the resistors go? Is it ground?
What voltage is the other end of your sensors? I assume it is 12V. If so that arrangement will fry your arduino as you can't put more than a 5V signal into it.
You have to use a resistive potential divider to stop the inputs from being driven too high.
It is a good idea to put some protection on the inputs as well, something like the circuit with the zener diode in this link.
http://www.thebox.myzen.co.uk/Tutorial/Protection.html
This is not the easiest of projects for a beginner. A car is a hostile environment when t comes to power, there are lots of sources of noise that could cause interference. Do some simple projects first and get some confidence before embarking on this.