Below is a list of the Function keys and their assignments applicable to this model. F0. Lights on /off (if fitted) F1. Sound on/off F2. Horn 1, two tone F3. Horn 2, two tone F4. Single horn F5. Doors close F6. Doors open F7. Driver/Guard buzzer F8. Flange squeal F9. Shunt mode F10. Acceleration/Decelleration override F11. Aux 1 F12. Aux 2