Member Credit: Mr DoLLa aka Raul

When you remove your OEM radio, there are 4 plugs that plug into the radio. Only 2 of the 4 connectors are used with your new aftermarket radio which are the 2 connectors with the larger size pins. The other 2 are not used but the VSS wire is the brown wire located on the larger of the 2 connectors not being used.

Definition: Vehicle Speed Sensor (VSS) via Crutchfield

In addition to the standard power and ground leads, remote-mount navigation (and even some in-dash units) systems connect to a vehicle’s Vehicle Speed Sensor (VSS) wire. Your vehicle’s cruise control uses the VSS wire to determine the vehicle’s speed — it serves the same function for the navigation system. (Don’t substitute the tachometer signal wire for the VSS wire — the tach signal wire sends pulses as long as the engine is running, even when the car is sitting still.) The VSS wire sends a series of pulses (from 800 to just over 1,000 per mile) only when the vehicle is in motion. If the VSS wire is not hooked up, the navigation system will not realize that the car is moving at all, and will be unable to track position.