The following assumes that the front signal lights aren't working either:
The signal lights are on fuse 4, the brake lights on fuse 5. However, fuse 4 also services the fan and voltage regulator, so if the car is charging, you don't even have to check the fuse.
Check the connectors at 8 in the wiring harness, and the connection between the gang connectors C and D.
And the flasher.