Instructions
Standard Sync
Turn on the Wii, and remove the SD Card cover on its front.
Slide off the Wiimote's battery cover.
Press the sync button hidden inside the Wiimote's battery compartment. The light on the controller will start to blink.
Press the sync button near the Wii's SD slots. When the Wiimote's light stops blinking, the controller is synced with the game console.
Repeat the process for each Wii you want to sync.
One-Time Sync
Turn on the Wii, and press the "Home" button on a Wiimote that's already synced to the console.
Click the "Wii Remote Settings" option on the Home menu.
Click the "Reconnect" button onscreen.
Press the "1" and "2" buttons simultaneously on the Wiimote you want to sync. The light on the controller will flash, then hold steady once the Wiimote is synced. You can sync multiple remotes this way, with player order determined by how quickly the buttons are pressed on the Wiimote.