In all the harnesses I know, blue with white tracer is only hot after ignition switch, at the on position. That wire feeds voltage regulator, spark ignition, and instrument voltage regulator only. No way related to the starter.We are taking baby steps here over several days. Your post #22 suggests you have power to big stud of starter relay, good. Next there is a dark blue wire with tracer (A1B), it goes from that starter stud to bulhead terminal Z. On the inside it goes to ammeter red connection. Check if that is good.......
So this 66 harness is totally greek to me or a wiring diagram is wrong ( wouldn't be the first we've seen ).















