This paper presents developments on Hybrid Electric Vehicle (HEV) prototype design from the viewpoint of electronic interfacing to the accelerator pedal, clutch and brake while assuring safe operation of the vehicle and maximizing fuel efficiency. The presented interface design has been implemented during the stage of modifying a front wheel drive commercial vehicle into a four wheel drive HEV. The demand for developing vehicle with improved fuel efficiency necessitates an intensive modification of its electronic and mechanical structure to maintain the electronic safety system of the vehicle. HEV technology is a promising solution for reducing fuel consumption and pollutant gas emission levels. The selection of drive train configuration and its suitable components, the design of the electric and electronic interface circuits that should he able to interface with power-train control unit as well as the overall vehicle control system are the main issues in the system retrofit procedure. Diverse configurations and hybrid component selections highly influence the integration process as well as the overall performance results expected from the vehicle. Electric and electronic circuits, which are integrated for implementing the hybrid controller for both traction and regenerative braking purposes via CAN interface using Rapid Control Prototyping technique offered by dSPACE digital signal processor, are presented for a second generation prototype Ford Transit hybrid electric van.