Trouble implementing a new controller in an existing project.

[eluser]henryboy[/eluser]
OK, so I'm new to Codeigniter, but I've been programming for many years.

Here is my issue. I'm working on some existing Codeigniter code, I am trying to implement a new controller but cannot get it working. Right now I have 2 existing controllers that do work. Controller1 is set to default and works fine. The other works by accessing it at site.com/controller2/. So if I copy controller2.php (contents is just a simple hello world index function) to controller3.php, and edit the class name should I not get a working site.com/controller3/? Currently it defaults to a custom file not found page.

Where do I need to look first to find out where things are getting redirected?