I changed the switch and it worked for a little while
It is possible both bulbs are burned out. The filament in each bulb should be tested with an ohmmeter. The bulbs can also be powered off the car to see if both filaments work but be wary of short circuits if you try something like that. Best to let a trained person deal with it. If the bulbs are good, check for corrosion and/or faulty connections in the bulb socket, wiring, and/or terminals. Finally, check for power at the bulb socket. If there is no battery voltage, obviously the circuit will have to be traced to find the fault which includes high resistances that could be causing a voltage drop. Also, check the ground. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a brake light bulb/circuit diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.