When I bought a second controller (wii-mote) for my Wii, I couldn’t figure out how to add it so that my Wii would pick it up. The instructions included with the controller and the console were useless. I figured it out though…

1. Open the front door on your Wii.

2. Open the battery compartment on the second controller.

3. Press the Sync button on the Wii inside the door.

4. Press the Sync button on the controller inside the battery compartment.

Eventually, the 2 devices should find each other. If you’re visiting a friends house, you can perform a one time sync of your controller to your friends Wii.