What would cause my brake lights not to work if not the switch or fuse?

- Damaged or burnt wiring

- Bad or corroded earth connection in the brake lamp cluster

- Failed bulbs. (although it's unlikely that all your brake lights have blown)

You can use a meter and a volunteer to check that power is reaching the bulb holder. If power is reaching the bulbs and they are working, then a bad earth connection may be the cause. Corrosion around the lamp cluster is a common cause of this. There may be problems with the other lights if the vehicle has a shared lamp cluster

At any rate, it wouldn't do any harm to let a vehicle electrician take a look