Don t know if you ve already found it... I mention it anyway for future surfers...

I was looking for the same, and found this piece of code :

<script type="text/javascript"> 
    function trackConv(google_conversion_id, google_conversion_label) {
        var image = new Image(1, 1); 
        image.src = "//www.googleadservices.com/pagead/conversion/" + google_conversion_id + "/?label=" + google_conversion_label + "&script=0";  
    }
 </script>

Then for links which you want to track just do this :

<a onclick="trackConv(1234567890,  LQV8CNq6RxCKlPbvAw );" href="http://www.example.com">Link</a> 

It appears that Google now offers an onclick option that you can copy and paste from the Conversions page in AdWords. From the AdWords Conversions page:

Add the tag to a button on your website, such as a "Buy now" button.

Here s a snippet from the page of documentation entitled Track clicks on your website as conversions. Replace XXXXX with conversion ID and label:

<!-- Google Code for Conversion Page
In your html page, add the snippet and call
goog_report_conversion when someone clicks on the
chosen link or button. -->
<script type="text/javascript">
  /* <![CDATA[ */
  goog_snippet_vars = function() {
    var w = window;
    w.google_conversion_id = XXXXXXX;
    w.google_conversion_label = "XXXXXXX";
    w.google_remarketing_only = false;
  }
  // DO NOT CHANGE THE CODE BELOW.
  goog_report_conversion = function(url) {
    goog_snippet_vars();
    window.google_conversion_format = "3";
    var opt = new Object();
    opt.onload_callback = function() {
    if (typeof(url) !=  undefined ) {
      window.location = url;
    }
  }
  var conv_handler = window[ google_trackConversion ];
  if (typeof(conv_handler) ==  function ) {
    conv_handler(opt);
  }
}
/* ]]> */
</script>
<script type="text/javascript"
  src="//www.googleadservices.com/pagead/conversion_async.js">
</script>

And somewhere else in your code

button.addEventListener( click , function() {
  console.log( Button clicked! );
  goog_report_conversion();
});

I ve a similar problem.

The Problem: My client have a contact page that have a form. After the user fill all the form fields, there is a validation(to check if the user filled correctly all the fields). After the validation, the user is redirected to the webmail server page. There isn t an "Success" or "Thank You" page. So i needed to put the Adwords tag, after the form validation.

The Solution:

The validation was done this way:

var missinginfo = "";
var f = document.forms["CONTACT"];
if (f.name.value == ""){
missinginfo += "
     -  name";}
.
.
.
if (missinginfo != "") 
{
missinginfo ="_____________________________
" +
"Empty Field" + "incorrectly filled" +
missinginfo + "
_____________________________"
alert(missinginfo);
return false;
}
//End of Validation

So i added this snippet code:

else if(missinginfo == ""){   //Check if the form was filled correctly
adw_conv();  //Function Name
return false;
}
function adw_conv(){
var img = new Image()  //Creates an image using JS to make the request
img.src = "http://www.googleadservices.com/pagead/conversion/123456789/?label=-8bcaCNHv6AIQl_v8_QM&guid=ON&script=0"; 
img.onload = function(){    
var form = document.getElementsByName( CONTACT )[0];
form.submit();
}}

This way, after the form validation and before the website redirect the user to the webmail page, is triggered the Adwords Conversion!

Google Conversion Tracking concept using Ajax on a submit button :

 $.ajax({
        type: "POST",
        url: "enquiry-submit.php",
        data: data,
        success: function (result) {
          $("#msg").fadeIn(400).html(result);

          /* Conversion Tracking Start */
          var google_conversion_id = YOUR_CONVERSION_ID_HERE;
          var google_conversion_language = "en";
          var google_conversion_format = "3";
          var google_conversion_color = "ffffff";
          var google_conversion_label = "YOUR_CONVERSION_LABEL_HERE";
          var google_remarketing_only = false;

          $.getScript( //www.googleadservices.com/pagead/conversion.js );

          var image = new Image(1, 1); 
          image.src = "//www.googleadservices.com/pagead/conversion/YOUR_CONVERSION_ID_HERE/?label=YOUR_CONVERSION_LABEL_HERE&guid=ON&script=0";  
          /* Conversion Tracking End */
        }
      });

It is 100% working on my Google Ads Campaign.

Note: You must Test this by clicking on your ad. The effect of conversion will be visible after 12 minute on your AdWords Console

Add the code below to the section of the page you want to track conversions on.

<script>
function adwTrack() {
   var img = new Image(1,1);
   img.src =     "https://www.googleadservices.com/pagead/conversion/XXXXXXXXXX/?value=1.00&amp;currency_code=EUR&amp;label=XXXXXXXXXX&amp;guid=ON&amp;script=0";

}

Just replace the XXX… with your actual conversion id and label.

Then call the adwTrack() function we created above in your link’s onclick event:

<a href="#" onclick="adwTrack();">Track This</a>

You can also do this using GTM: https://www.redflymarketing.com/blog/track-conversions-without-a-thank-you-page/