If your reverse lights aren't working AND your dashboard reverse indicator light isn't either (assuming bulbs are ok) this thread may be of help to you:
[URL="http://www.toyotanation.com/forum/showthread.php?t=272634"]
The discussion is on the 4-cylinder and it's automatic transmission, but may be somewhat relative to yours.
Also, see manual "A541E Automatic Transaxle - V6 Automatic Tansmission (4.76MB)" here:
http://www.camrystuff.com/index.php?page=Gen3_Manuals
Especially pages AX2-118 diagram 2, and AX2-16.