1971 dart Only cranks when I jump the relay.

It's the _brown_ wire from the relay to the neutral safety switch that you'd need to ground to see if a bad NSS or related fault is causing your problem. The yellow one is relay +feed from the starter contacts of the ignition switch. If removing the brown wire from the relay and grounding that relay terminal lets you crank the engine with the key, it's a bad NSS, a bad brown wire, or (you hope not) a problem with the actuating finger on the rooster comb inside the transmission. if that test doesn't let you crank with the key, there's a problem with the ignition switch or the wiring from the ignition switch to the relay.