Neutral safety switch and back up light questions

[2labman]

I'm new to this site and forums in general. But I have a 71 blazer that I've been in the process of installing a painless harness in and a question. I know that the nss has wires coming from the two purple wires and backup lights however I don't know where the back up lights are coming from or going to, what color they are, or how this nss even works. The truck is a manual and didn't even have the nss in it so I bought one but don't know how to hook it up. All I know is the truck won't start now even if I just plug in the two purple wires but will if I put a wire connecting those two wires. Any help is appreciated
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