The year_make_model.php file was modified to work with the All Products contribution (if installed)
So if you are on the home page and click the "Go" button you will see all the products for selected year, make, model.
The All Products contribution can be downloaded from - http://addons.oscommerce.com/info/1501
Download the contribution and view the screenshots to better understand this version.
The autoinstaller script requires PHP5