How to make a fan switch ...need help!

[vegetoking]

Hey guys i wanna try running a switch into my dash to turn the cooling fan on and off whenever i feel is necessary... i was just wondering if someone here would be so kind to hook my up with a list of materials and info on how to make one.

Ive searched but all i can find is bague ideas. I need to know specific grounding points and a specific hot wire i can connect the wire coming from the positive side of the fan to. thanx again!

Also will this damage the fan motor? Do i need a transformer or something to prevent it from getting too much volatge?