Backup lights do not work. Everything else is fine. How can I fix this?

the way the tail lights on a 2004 JGC are the wiring is actually located inside the light housing itself - the only way to determine if problem is in tail light is with a OHM Meter to see if coninuty is there, and also check to see if your getting power to the lights, if no power you have broken wire somewhere - but most likely you will have to replace the Lighting Housing - this is a BAD design and shorts inside the housing are common - the short can't be fixed at all the wiring is inside the plastic ....