Hi,

Be aware that in some cars the analog signal goes to
the electronic speedometer/odometer where it is used for
the speed and distance indication, and then the same
signal (TTL now) leaves the dashboard and goes out to
other ECU's of the car.

Example:

You can open or close the retracting roof of a
convertible (cabriolet) only if the speed is below 30 km/h.

Best regards,

Luciano