I am trying to get a page to update a selection of php mysql results via ajax.
I can get this to work with only 1 dropdown list but I have a maximum of 14 inputs the user can choose from to filter the results. I am using the following script on the page to call the .php page which runs the updated query on the table and returns the filtered results.

The javascript I have on the page which is called using onchange on one of the dropdowns is:

Code:
<script type="text/javascript">
function showCars(str)
{
if (str=="")
  {
  document.getElementById("txtHint").innerHTML="";
  return;
  }
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","getcars.php?q="+str,true);
xmlhttp.send();
}
</script>


I need to get a selection of form inputs to generate a url similar in style to the one shown below:

getCars.php?Make=Claret&Model=2005&Tophats=Funny


Can anyone show me how I can achieve this please? I think if I can bget this bit to work I will be able to sort out the other issues I have with the site I'm working on.

Any help would be extremely appreciated, thanks in advance!