There was not enough information in the first few posts and then the information after is kind of scattered.

How I would do this, IF I think this is going, is to isolate that wire he has voltage on. See where its getting its 12 volts and remove it.

The Neutral switch lug on the Starter Relay, I would just make a 5 inch black wire with a female spade on one end and an eyelet connector on the other. Put the spade on the neutral lug and the eyelet under the bolt holding the Starter Relay down, BOB's YOUR UNCLE!