Execution order
1. If the brake light does not come on, first check the fuse in the fuse box.
2. If the fuse is OK, check the lamp and replace if necessary.
3. Check the brake light switch. To do this, remove the cover above the pedal. Disconnect the brake light connector.
4. Turn on the ignition.
5. Connect both contacts in the brake light switch plug with a short wire. If the brake light now lights up, the fault is in the switch. In this case, replace the switch with a new one, referring to the subsection Removal and installation of switches and lamps.
The original material is located on the website AudiManual.ru