Wiring up a neutral safety switch

I need some help. I'm wiring up a neutral safety switch in my '72 Demon and I need to know where the wiring needs to go. The car was originally a manual trans from the factory and there's no harness to plug into the 727 that we have. I'm pretty sure that one of the wires goes to a terminal on the starter relay, just not sure which one.I'm using a Hurst Pro matic 2 shifter. If someone could help out or show a diagram, that would be great.