2000 SL tail light/back up light problem

I have a 2000 SL.

My left brake light recently went out, and I easily replaced that, and it now works.

However, I noticed during this that my back up lights (both left and right rear) do not work, nor do the tail lights (except on the brake light segment, which is the lower part of assembly). I replaced the back up bulbs, and they still don't work. I checked the fuses, and didn't find any that were blown.

Here's a crude diagram to illustrate what I'm trying to say:
http://i95.photobucket.com/albums/l147/pointyskull/tail.jpg

Any theories on how I can rectify this?

thx!

I have read other forums and found there is one more thing to check for the reverse lights: the reverse switch on the transmission. When putting the transmission in reverse, the switch may not be transmitting to the light.

I am here to ask how to find this switch and fix it too...