Blower motor cuts out

Hey guys, I’m working on my 1975 Dodge Dart swinger, 318, auto, with factory ac (let me know if I missed anything). I finally found the correct blower motor wire and got my heater working today for the first time in five years... except the blower motor cuts off after 5 min of running. If I cut the blower motor off and let it rest after a few minutes it will cut back on and run for another five min or so. I’m getting power everywhere except after the pigtail where the blower motor connects to the harness going into the blower motor. When the motor is running I have power everywhere including at the pigtail going into the blower motor, when it cuts out I lose power at the pigtail only. What am I missing? Thanks for any help. Oh and my fan speed selector switch works when the fans running and the slider to select vent, ac, max ac, heat works as well when the motors working.