My Dart Swinger Project!
Last time I had a starter relay go bad all of a sudden like that, I think it must have lost connection to the neutral safety switch terminal on the inside somehow. I rigged up a jumper wire to go from that terminal to a ground, and the car fired right up. If I remember right (been a minute) it is the terminal kind of towards the bottom of the relay, and is the one closest to the firewall. Usually has a wire with a plug that wraps over the side of the relay.....and I think a yellow wire? You could try rigging a jumper wire and see if it turns over, then go buy a new relay if it does. Dang, I wish I was close enough to come give you a hand! If the ol rusty truck has enough gas in it....let it charge the battery for a while. Hang in there dude....you'll get it! :)