I have been attempting to use  The Quick Email Button to help me create a button in a custom object that will generate an email.  I have successfully created the email button and the email template, but when I click the email button none of my merge fields are populating in the email.  What am I doing wrong?

Here is the code I have set up:

location.replace('/email/author/emailauthor.jsp?retURL=/{!Candidate_Tracker__c.Id}&template_id=00X50000001Ri74&p5=');

Thank you!