Loading external swf - won;t display?

programming flash
1

I have the following code in the first frame of my fla which also contains the empty movieclip mcWheels:

// Include Flash functionality
import flash.display.Loader;
import flash.net.URLRequest;
//import flash.events.Event;
import flash.events.MouseEvent;

// Define variable
var url:URLRequest = new URLRequest();
var loader:Loader = new Loader();

// Load the parts movies
url = new URLRequest("wheels.swf");
loader.load(url);
mcWheels.addChild(loader);

If i do a trace(mcWheels.numChildren) it outputs 1 so I’m assuming the file has loaded correctly. However the contents of the external swf are never shown… Please help :frowning: