Instructions
Standard Mode Registration
Turn on your Wii console by pressing the power button. Open the SD Card slot on the front of the Wii. You can find the flap covering the SD Card slot directly left of the disc slot if your Wii is standing upright.
Take off the battery cover on the back of the Wii remote you want to register. Press the red "sync" button next to the SD Card slot, then press the red "sync" button on the back of your Wii remote.
Watch the "Player" LED light on the front of the Wii remote until it stops blinking. Once the blinking has stopped, your Wii remote is now registered to your Wii.
One Time Mode Registration
Press the "Home" button on a Wii remote already registered to your Wii console. Go to the bottom of the screen and select "Wii Remote Settings".
Choose the "Reconnect" option, then hit the "1" and "2" buttons on the front of your unregistered Wii remote simultaneously.
Watch the "Player" LED light on the front of the Wii remote until it stops blinking. Once the blinking has stopped, your Wii remote is now temporarily registered to your Wii. This registration will expire the next time your Wii console is powered off.