its as simple as running a wire from the positive battery terminal (or equivilant) to a switch then run the other terminal from the switch to the positive on the fan and grounding the negative of the fan to the negative battery terminal.
you may leave the original connector on and simply tap the power from the switch to the power line for the fan and leave the existing positive and negative. this way your fan will come on when the coolant sensor tells it to and/or when you flick your switch.... that would be safer as if you forgot about it would still come on.
