Neutral safety switch

[2labman]

I've got a 71 with the 4 speed manual and I'm putting a new painless harness in it, I can't figure out how to wire the neutral safety switch. Everything I'm reading is that there are 2 heavier gauge purple wires that plug into it and 2 green back up lights but I don't understand where the b/u lights run to from the switch, where the switch gets its power from or how come when I just plug in the purple nss wires the truck won't start but when I just put a jumper wire between the 2 purples it will start
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