no start after sitting

69 dart 360, 727
turn the key and there is nothing. put car in neutral and tried to start it, nothing. pulled the neutral safety switch ground wire off the starter relay. ran a jumper wire from the starter relay nss ground terminal to the ground on the battery and the car fired right up. Once started it will fire up every time. after it sits all night it won't start.

feel stupid not knowing how to test if its a bad starter relay, NSS,or wiring issue.