Brake light works, but tail light doesn’t. Bulb is fine. Diagram use: Shows that the tail light receives ground through a separate brown wire (pin 4) that often breaks inside the hatch hinge loom. Diagram helps you bypass with a new ground.
Most owners feel intimidated by factory diagrams, but they follow a logical structure. Here’s how to decode them: peugeot 308 wiring diagrams
You have the diagram. Now what? Follow this process: Brake light works, but tail light doesn’t
PSA (Peugeot-Citroën) uses an internal system called (Schémas Electriques et Diagnostic des REseaux). If you ever get access to this (via Diagbox or Peugeot dealer), you can: Brake light works
Many sellers offer PDFs of Peugeot 308 electrical manuals for under $10. Verify they include the correct year (2008 is very different from 2015).