Wiring electric fan.

[Popp55]

So I just need help on how to wire in my electric fan. I put a new motor in a few months back and now when I give the truck gas my fan flexs too much and starts to hit. I've already put a spacer on it and it didn't help. So I decided an electric fan would be my next option. This truck was a project from my grandfather for the both of us until he passed away. So I've been going at it with basic knowledge but wiring is not my strong suit. I'm just curious on where I can connect it as far as the fuse box and if I should run it to constant power with an on/off switch or just power to the ignition if that makes sense.. truck is a 1972 C10.. thanks!