Here is what I went through, hopefully it will save you some time.
The first thing I did while the Wii was turned on was that I tried to sync the Wii Remote by pressing the "1" + "2" buttons at the same time
. The lights at the bottom of the controller flashed for about 30 seconds, but never received the signal from the Wii. Bummer.
The next step I followed was to hit the sync button on the Wii Remote (Wiimote). Then immediately opened the cover for the opening where the SD Flash card goes and pressed the sync button on the Wii. 30 seconds of flashing, and no result. Double bummer.
Finally, after some Google searching, I found a couple of message boards where people had to press the Sync button on the Wii (not the Wii Remote) for 15 seconds to reset it. I performed this step and then pressed sync on the Wii Remote. The 2nd controller synced up almost immediately. What a relief!
Apparently the problem lies in the fact that the Bluetooth technology
being used has to be manually synced in order for it to connect to the Wii. It does not make much sense at all. You would think they could be pre-authorized in order to minimize time and ease of use. In addition, you really have to be careful that your other controllers are turned on while syncing or else the controller that you are trying to put on channel 3 might end up on channel 2! This happened to me on one occasion.
Good luck with getting your Wiimotes in sync with your Wii. Hopefully this helped!