Everything was going so good

My car (70 Duster 340) has been pretty dependable for a while now but now I'm having issues. Car fires right up after sitting for a week or two. Take the car out for a drive and everything is great. When I park is when the issues start. The other night I went to a local cruise and was there for a bit. When I went to leave my car would turn and turn and turn but wouldn't start. Spark was definitely the issue. Tried checking for loose connections and saw nothing obvious except my negative battery cable to the drivers head was loose. Anyways killed the battery and called AAA like I used to do so many times when I first got the car but not for a while now. Someone at the cruise offered a jump while waiting for AAA and the car fired up. I cancelled my flatbed ride home and drove home without issue. I took my car out again last night and drove all over without issues till I got home. After parking the car I went inside for about 20 minute and then went to try and start my car.....Same thing, turning over fine and no spark. Again checking connections found nothing out of the ordinary but turned the key and with the gas to the floor she fired up....ran fine but when I turned the key to the off position the car would not shut off. With the key in the off or aux position the car was running. I had to stall the car out to shut it off......Then I turned the key and she fired right up and turned off like normal. I started and turned off the car 5 times before heading back inside....I plan on taking a good look over the weekend but not even sure where to start at this point.