You dont want to do the toggle switch method unless your car is seldom driven. At least put a controller (even a cheapie) on there and have a manual fan switch override (I think this is requisite for all cheap fan controllers anyhow). That way if you forget to flip the switch, hopefully the controller saves ya.
A quick search will really reveal more than you wanted to know, along with diagrams and all sorts of neat stuff (I hate it when people say to search, so that tells ya how much stuff is out there).
Good luck.