I have a 92 Chevy Caprice. Advice where to go next. Top middle brake light works, tail brake lights wont work. I have replaced the switch behind the brake pedal, fuses are good. Ground wire next?

Check the bulbs? & look for wires (ground) that need to be cleaned up. Verify that there is power in the bulb socket with a simple test light. Brake switch is working if top middle break light comes on.

I was going to mention that the break lights to the rear lights are two different circuits. Start with the bulbs, ground wires, and then do you have power to the lights when the break peddle is applied. If not go forward towards the fuse. If you have power before the fuse, it may be the fuse or fuse connector. You can start from the fuse and go from there and work backwards. First is to buy new bulbs and replace them, cleaning the connections with emory paper to clean the contacts, then make sure the ground is clean and connected. If it does not work, power to the lights? Check the wire if you don't have power. Work forward a this time toward the fuse, or last place you have found power. Remember, the break peddle must be applied to send power through the electrical circuits.