/6 swap for 318 now it won't even turn the starter? nuetral safty switcch?

169Dart4Y, I had exactly the same problem with that yellow wire in my '62 Valiant! Boy, was it hard to troubleshoot. I believe that yellow wire will sometimes become shorted to ground for some reason, but I'm not sure exactly why. Mine had obviously been shorted because all the copper in the wire had become copper oxide from overheating, and it didn't conduct well at all. I'm afraid you might have to replace that yellow wire completely before it will start reliably.