I had no reverse lights for a couple days. There is a little switch under the jeep that i believe has 3 prongs, it just looks like a nut with a rubber cap and wires running to it. If you can bypass it and the reverse lights come on, it's bad. I think mine was $20 to fix through the school, and only took 10 minutes or so. I dont remember where it screws in to, but for some reason I'm thinking it's the transmission fluid pan. When you unscrew it tranny fluid (i think) comes pouring out so you have to screw the new one in fast.
Then again I did it on a lift, so that made things easier.
'93 Grand Cherokee Larado 4.0l - 4wd - Wrecked.