Speedometer Signal Converter Module

This is a simple module that will convert the speed output signal from the 3800, 3.4DOHC, Cadillac Northstar, or 4.9 ECM to a signal that can drive the Fiero speedometer. The module is extermely small and can be easily integrated into your wiring harness. Operational explaination: The Fiero uses a gear driven variable reluctance magnetic type VSS that produces 4000 pulses per mile in the form of a (relatively) high voltage sine wave. The driven gear can be changed to compensate for different tire sizes. The VSS signal that is sent to the instrument cluster where it is buffered and distributed to the meters (speedometer/odometer) as well as the cruise control module and engine control module. Most other GM vehicles such as the ones that are commonly used for Fiero engine swap donors, operate a bit differently. An approximately 24000 pulse per mile speed signal is generated by the VSS and sent to the ECM first. The ECM is calibrated for the specific tire size. The ECM buffers and divides the signal and distributes it to the appropriate modules and the speedometer in the form of a low voltage square wave. The signal that is output by the ECM will not directly drive the Fiero speedometer. If you are doing a Fiero engine conversion and using this type of system, you will need a signal converter to make the speedometer work.