Ok on this assembly the top light isnt working is what your saying or the very bottom doesnt work
I think what the OP is saying is that the third brake light...high up above the flip-up glass....is working but the two lower brake lights ie. left and right...are not working.
The power to all three brake lights is common so obviously the brake pedal and fuses are OK. The third brake light though has a different ground to the two lower bake lights so the ground could have gone missing to those failing lights.
@JessK4283....what year is your KJ....I will look in the circuit diagrams to see where the ground for those brake lights are supposed to go.
Edit to add: If your tail lights/turn signals are working then it is probably not the ground as the bulbs in the cluster share the same ground.
What is different to the third brake light and the left/right brake lights is that the latter get their power via connector C310 pin 6. This connector is located in the rear load area on the right side, just below the rear power outlet,behind the plastic cover. It is a light grey connector and the wire you are looking for is a White wire with a Tan stripe.
You ideally need a Multimeter to check at the rear brake bulbs if there is +12 volts on the base of the brake lamp...White/Tan wire...when the brake pedal is jammed down. If the +12 volts is there then maybe you need to clean the bulb housing well in case you have a bad contact...either on the bulb base or the grounding point of the bulb.
If the +12 volts is not there then you need to trace that White/Tan wire to connector C310 and check if the voltage is on both sides of the connector..maybe re-plugging that connector fixes the problem.