Gauge Indication Systems: Speedometer
WARNING: This page is about a different car, the 2002 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
The Output Shaft Speed Sensor (OSS) generates and transmits the Vehicle Speed Signal (VSS) data to the Powertrain Control Module (PCM). The PCM sends the VSS data through circuit 679 (GY/BK) to the instrument cluster and all other systems that require VSS input. The instrument cluster, upon receipt of the VSS signal, commands the speedometer pointer to the corresponding position.