Originally Posted by dakotadigital

The SGI-5 Universal Signal Interface Unit can handle nearly any of your electric speedometer signal conversion and calibration issues. The SGI-5 can recalibrate 2,000 pulse per mile (ppm) through 250,000 ppm electronic speedometer pulse rates, either up or down. The SGI-5 is great for adjusting aftermarket and OEM electric speedometers on vehicles after changing rear end gears, tire sizes, or drivetrain changes affecting the speedometer.
The SGI-5 is used as either a signal multiplier (up to 4X) or signal divider (up to 125X), making this unit extremely flexible for almost any application. While the SGI-5 is intended to correct only the signal feeding the electronic speedometer, in many cases where a speed signal is shared or on a databus, the SGI-5 can instead correct the signal feeding the engine and transmission computers.

If your vehicle is equipped with an anti-lock braking system (ABS), it is generally advised to ensure the signal reaching the ABS controller is not altered to eliminate any potential problems affecting control algorithms within the system. Some vehicles also utilize the output shaft speed to calculate transmission slip and lock-up. When a signal feeding the PCM is altered, this may cause the PCM to detect a constant slip. Consulting a service manual may be of assistance in determining the signal routing within the vehicle if the SGI-5 is decided to be used in a situation such as this.