69 340 problems

You say the car tries to start when you let off of the key and put it in the run mode? I had this problem with my car. I had something wrong in my switch that wasn't sending power to anything but the starter in the start mode. Put the key in the run mode then jump your selonoid. It worked on mine hope this helps. If it works their is something wrong with your switch, Mine had a pushbutton ignition on it now so its fixed. Probably won't work but its an easy try. Good luck Rick