New battery and alternator, headlights wont work and car wont stay cranked

Hello, have you determined if your vehicle has an engine performance problem or an electrical issue with your starting and charging system? An engine problem where it is stalling due to performance issues can create an idle speed so low that components may not work as needed. But it is far too difficult to guess about without hands on inspection. Of course, the starting and charging system beginning with the "new battery" should be tested to ensure all components are functioning as designed.