1972 Duster 340 Car, Electrical problem

Good afternoon all, "1972 Duster 340" rebuilt nearly entire car, now when I start the car it run, poorly but it does run, until I close the driver's door or turn the headlights on and than the engine dies??? Turn them off or open door and it can be started again. Also can't locate the wire that needs to go to my neutral safety switch on transmission. Could use a little help with this.