[davepl]

The purple wire is the wire that carries current from the ignition switch to the starter solenoid. So any interruption of that circuit will act as a neutral safety.

Wire it to the provided neutral safety in the new shifter and you should be set!

I strongly encourage you to solder and make any connections in this wire PEFFECT, including any old cuts or splices from previous owners. If the purple wire is anything but perfect, you'll find that NOTHING happens when you go to crank it on a hot day.

That's the famous "Chevy Starter Heat Soak" problem and people throw starters and heat shields and all kinds of parts at it, but it's usually just a bad connection in the purple wire.