using jquery ajax POST method returning 500 error

[warroyo90]

Zen Cart is set up to prohibit access to any ".php" files located anywhere inside/under the /includes/ folder.
You will need to put your script someplace else. It cannot sit in /includes/templates/ nor anywhere else under /includes/

I also tried putting it in the root directory and it still returned the error. I tried including a php file that connects to the db without using the global $db object but when I run a query for example

$query = "SELECT products_model FROM products WHERE products_model = '$partNum' LIMIT 1";

$result = mysql_query($query);
$row = mysql_fetch_assoc($result);
print_r($row); 

I do not recieve a 500 error but the query returns no results. so with this said how can I make an ajax call to a php file that runs a query in zen cart ?