Electrical System Flunked

Hey all. I just got my first project car!! A 1974 Duster with a 225 and automatic transmission. One of the things that need fixing in this baby is the electrical system. I was told that the headlights some times work (though i haven't tested them yet). The blinkers never worked with me and I presume the brake lights are also duds. The car has a separate button that needs to be pressed while the key is turned to start it. Also the battery drains if left plugged in. What is the best route here? A new harness? And how do I get it to start with just the key?