Funny how answers are all over the place. This is a 1970 car. So it should have a safety switch. Having said this, the owner has not really provided good info. Is this an Auto car swapped to manual or a manual car swapped to new TKO manual?

A manual transmission does not have a safety switch. It has a backup light. The safety switch was on the clutch petal as explained. Did you remove that too?

It really is simple, you add a ground wire and it works. Since you want to use brain instead of safety switch, keep the ground you attached in place. Your done. I already explained why in an electrical circuit you see voltage even if the circuit is not drawing current.

You next problem is dash lights if it still exist.