Autopilot?

Ok heres the deal my bud has a 73 Dart Sport with power steering. When we got the car it was spraying fluid out the top of the box where the lines go in- no problem just needs some new O-rings, finally got her all sealed up and it became auto steering- you would start it and the wheel would just turn all the way until it stopped. So I thought something funky with the box and I pulled one out of my 74 4-door which I kney was good and its still acting about the same- I told him it the pump or maybe the return line's blocked. I'm stumped honestly I'm just making an educated guess. If anyone has any ideas let me know because its plain scary to drive.