What fuse should I change?

The system that has to do with backup lights in cars is pretty standard. If they are not protected by fuses the problem may lie in the backup switch . If fuses are involved check them with a continuity tester. The switch closes a set of contacts when you depress the brake. It is located in most vehicles close to the brake pedal. If you dont find it , get a manual for you Jeep model .Here they will tell you where to look for it. Test the switch . When out of the car it will be normally closed. If its ok then check the wiring and the bulb sockets.

It should be a 20 amp fuse, third column from the left, second down in the fuse block under your instrument panel. I also suggest getting a Chilton or Haynes manual. I've got a 96 Laredo with 178,000 miles that I bought right out of high school, and she's still riding strong.

re-check the manual if you have one, other than that you could pull each fuse out one by one and see which one it burned, if none of them, call an auto store and ask them or the jeep dealer

You can try to contact a Jeep dealer to get the owner's manual, but they'd probably have to order it or contact someone.

But...try these sites. I do this with every car I buy--find user forums. You can usually find someone who's had a similar experience by looking at user forums.

http://www.jeepsunlimited.com/forums/index.php

http://autotropolis.com/cs/forums/default.aspx?Gro...

http://www.autoweb.com/content/research/forums/ind...

check for burned fuse

the switch on the transmission is bad