Brake lights not working, but tail lights and centre brake light do. on 1998 Toyota Corolla

My tail lights work
The centre light comes on when brakes are pushed
Right and left brake lights do not.
I've checked the fuse and the bulbs and all seem in good shape. What could I be missing?

2 answers
Ground at the rear to the brake light bulb ground. Put a good known ground to the case of the brake light bulb holder, and try the brakes.
Also check the wire harness for open circuit (broken wire).