Throughout the evolution of transportation technology the automotive industry has continually devised methods of diagnosing and servicing vehicle electrical and electronic concerns. Methodologies have always included special test equipment accompanied by volumes of printed manual procedures. Today's vehicle technology, with its highly interactive/integrated systems control capability, has brought on a new level of complexity and confusion to the service technician. In order to assist the technician in the diagnosis of microprocessor based control systems, the service industry has developed highly sophisticated on-board vehicle diagnostics as well as off-board computer based equipment.This paper describes the progression of service test equipment provided by Ford Motor Company to assist in vehicle electrical/electronic diagnostics. Similar to all industry manufacturers Ford Motor has devised both on-board and off-board systems which are required to fix the car right the first time.