Installing new dash wire harness in 67 dart

I had a question on one of my harnesses from Laysons. The customer service there is good.
I called and spoke to "the guy" who actually modified my harness. I forgot his name but he worked on Saturdays.
He gave me alot of phone time, and helped me out tremendously, plus he is an A body guy, and owns a few. We were able to figure out the best way to make it work with my application.
I know you are talking about the ignition switch, but the point is, they have knowledge.
You may be able to get the best approach from them, or, like Kendog says, install the additional ground and be done with it.