Conversion tracking

I am still trying to build my forum and I use Google Adwords and Facebook for advertising to get traffic.

I want to be able to track these conversions. To do this I want to add the tracking specifically to the "registration success" page

But how can I do this?

I have looked in register.php but I am not sure how I can get the tracking code at the </body> tag for just the success page

Any tips please?