Erratic electrical problems

[turbodickie]

95 Mustang Cobra: New alternator, new ignition module, checked all grounds I think. Car runs ok without excess electrical draws but at night with headlights on, even turn signals effect the engine ops. ie. runs very poorly then.Will kill engine if idling and headlights turned on. Have tried everything I can think off to no avail so I need help. Car also hesitants when adding throttle. Have checked several times and NO codes show up. Cleaned the ground cables even put a new battery in this car. Thanks for any suggestions you may have