1. Turn off the engine and allow the vehicle to cool down.
2. Park the vehicle in a safe location and apply the parking brake.
3. Open the hood.
4. Locate the vehicle speed sensor (VSS) on the transmission. It is usually located on the driver's side of the transmission, near the firewall.
5. Disconnect the electrical connector from the VSS.
6. Using a multimeter, set to the AC voltage setting, measure the voltage between the VSS signal wire and ground.
7. The VSS signal wire is the wire that provides a voltage signal to the speedometer. The voltage will vary depending on the vehicle's speed.
8. Once you have identified the VSS signal wire, connect it to the appropriate input on the navigation head unit.
