Take apart XBox 360 using included iFixit guide to remove motherboard.

This part is a bit tricky as you have to apply a bit of force in Steps 21 through 25.

Once removed, identify pin header and voltage selection solder points with rgall0's guide.

If you want 12v then solder R7V7 together.

If you want 5v then solder R7V6 together.

Solder pin header to board (I only used 2 pins for VCC and GND).

I had to remove the smaller heatsink to get better access to the solder points.

Using rotary tool, cut opening for fan in top case.

It originally has a metal liner on the plastic case, so I removed this permanently which let me mount the fan directly to the plastic case.

Test everything before closing up the 360

Put the 360 back together, starting with the internal components and plastic, add the screws on the bottom of the motherboard, and then add the external housings.

Add all smaller silver screws to all the holes except for the 6 longer screws for the optical drive corners and plastic fan cover with longer screw holes.

The 8 smaller black screws go in the 8 holes beneath the chips in the middle of the board.

Add front button daughter board and apply 3 smaller black screws, covered with plastic power button cover.

Mount fan on plastic with 3 pin header connector (female).

I chose to have the fan blow air in to the case to allow more cooling, hopefully.

Finish closing up the 360 and give it another test.

The fan should go on right when you turn on the 360, and should stay on about 10 to 15 seconds after you power it off.