Car dying when the lights are turned on?

My little brother and I were going through his 74 duster this weekend. We changed the battery, alternator, and voltage regulator out with fresh components. Car runs well although when the car is idling and you turn the lights on(switch all the way out) the car dies. It only does this at idle. When cruising it doesn't. Was gonna take a look at the switch this coming weekend but figure Id ask here and see if anyone else has had a problem like this. Thanks guys.


James :burnout: