Very easy and quick to do.
Tools needed:
Drill
Drill Bit
Toggle Switch of your choice, I chose a simple black one to look sorta sneaky
Wire cutter/stripper or teeth work fine
A wire hanger
I bought 40ft of 18 gauge wire, which was over kill at wallmart for less than $2
A mini 10 fuse
Electrical Tape
I made the mistake of waiting to take pics when I was all done
Locate the loom above the PCM and cut it open and locate the blue/pink wire
Its the loom that now has the tape on it in this pic
A close up
I used a small knife and cut the blue wire and then use some wire you bought and attach one end to the fuse and one and to a grounding location with the car in the on position, if the fan turns on, you got it, now get that wire out of the way and use the hangar to run wire through the firewall, I went through the same place I have my radio hooked up, tape up the wire to the hangar and poke it through.
A visual
A close up, still difficult to see
Now take your drill and find where you want to mount the switch, I mounted it right outside the fuse box to attach the grounding wire where I have my wideband grounded.
Here is the switch, I scratched the dash a little because the drill I have is a piece of crap and it kept popping out.
Here is where I grounded it inside the fuse area
Very very easy if I did not explain it clear enough feel free to ask questions.