Good price GPS speed sensor supports negative and positive pulse output up to 50,000/km. It works at 8-32V operating voltage with a 1~2 years long life working period, specially designed for various speedometers and driving recorders.
Please connect a GREEN or BLUE cable (one of the two) to your current Speedometer/odometer/tachograph.
GPS Antenna: Securely fasten the GPS antenna, preferably outdoors (ar inside front windscreen) so that it has a clear view of the sky to pick up satellite signals.
Tips: How to program the speed ratio to fit your current speedometer/odometer/tachograph?