Where is the coolant fan temperature switch located?

I've been told that I need to replace my coolant temperature switch, so I bought one. My problem is that I can't find its location. Parts store couldn't tell anything.
My problem is that's leaking water, I think it's coming from the radiator plug. Engine coolant fan not working. Acc fan works only. I bought a fan for it. But if the switch isn't good, it still wont come on.