Depends what you have available. I had some old fans which didn't mind getting chopped up to use as donor wiring.
You will need:-
A fan controller. Cheap or otherwise.
A fan header connector with at least the red and black wire still fitted.
A pair of scissors.
A soldering iron (although using a screw type terminal block would be fine)
Cut off 4 pin peripheral connector (molex) leaving a few cm of wire at the end for future use.
Strip wire insulation back about 5mm on both red and black.
Do the same on the donor fan header connector.
Solder/join red to red and black to black. Insulate with tape.
Plug fan header into fan controller.
I find on my cheap fan controller ( off the bay ) that I get best useful range on medium tri-cool setting from maybe 600 rpm up to maybe 1500 rpm or so. On low tri-cool setting I found I could stall the fan if I dialed it down.
I currently have my front tri-cool set up with this mod.
Probably better to buy decent fans though. Tri-cools are cheap fans that make unnaceptable noise even at lowest settings, in my opinion.
