Well if you dont get the display to lite up and see the error codes on the computer is going to hart to know what is causing the problem, but to start check the battery have 48 volts if you dont have 48 volts going to terminal #1 and # 2 coming from the battery the display will not lite up check batt. plugs terminals on the truck side and batt, side if battery is full charge and still no display, replaced the computer