Step 1: Why I Did This
Today I was playing musical drives because I have a DVD-R and a HDD that really dont like each other, and I have a pile of CD's to duplicated (all public domain.) So I decided to swap the HDD for an extra optical drive.
When I pulled my computer apart I discovered that pretty much everything was hotter than I would like, especially the HDD's (I have 4) so I decided to shove a spare fan I had into the back of the case, I was too lazy too mount it next to the Hard Drives because it would mean pulling half the components out. When I turned it on the extra fan worked great, but it sounded like a vacuum cleaner and it wasn't really blowing air over the drives like I wanted so I decided to something more elaborate was in order.
Step 2: You Will Need
Some 12v Fans (I got mine from PSU's as they tend to be more powerful)
A 5 1/2 inch Blanking Plate
Some SPST 12v illuminated switches (or just SPST switches) 1 per fan
Hookup wire (must be good for 1/2 amp or so)
Mounting screws / bolts
Molex "Y" connector or female molex connector
Hot Glue Gun (optional)
Drill / Dremel Tool
The switches I used are from maplins which I intended to use for another project that never got started. See the closeup image for the pinout. You can use normal SPST panel mount switches and the wiring will be a bit simpler.
Step 3: Mark and Drill the Blanking Plate
The holes don't have to be too pretty as most panel mounting switches have a nice wide collar when they are fitted and cover up most mistakes.
Step 4: Make the Common Connections
If you have a 12v supply available at this point you can hook it up an test the switches, they should illuminate in the On position and go dim in the Off position.
If you are using normal SPST switches you will just need to make a common +12v on the back of your switches and then connect all your Gnd wires together later.
Step 5: Extend the Fan Leads
My connections are still only twisted at this point.
Step 6: Mod Your Molex Connector
After I took this picture I cut the red and other black wire right back and taped the ends so you basicly had a short little F->M lead with 8 of yellow and back wire coming out.
Step 7: Connect Everything Up
Connect the +12v (normally red) from the extended fan lead to the center pin of your switch. If your using normal SPST switches then just connect them to the other side. Repeat for each fan / switch combo.
Now connect All your GND wires from your fans to the GND tail from your switches. If you used normal switches then just connect them all together.
Then connect the yellow wire from your molex connector to the +12v tail on your switches
Finally Connect the black wire from your molex to the GND tail from your switches, or in the case of conventional switches to the collection of fan GND wires.
If you have a 12v supply you can now test your rig, each switch should illuminate and operate a fan independently.
Step 8: Solder and Make Good Your Connections.
When you have everything soldered nicely then you _MUST_ tape all your joints with electrical tape, if you don't do this then the first time a +12v connection shorts to anything you will probably fuck your computer, or at least your PSU.
An optional extra step is to hot glue over the connections on the back of the switches just to make extra sure nothing shorts. I do this with pretty much every permanently assembled switch I use because I think its good practice. If your switch has an open assembly then be careful not to get any glue inside because it will probably break it.
Step 9: Make the Cables Nice
Step 10: Install the Fans
I used the short fat little fan screw for 1 fan, but I didn't have any for the other so I used some little bolts that were just long enough to pass through the fan and the chassis. In my box the powerful fan blowers over the CPU / RAM and the quiet fan blows over the HDD's. I had to drill some vent holes in the plastic cover on the front, but most cases I've seen have holes here allready.
Step 11: Finished!
I've got a little hand held label printer so I knocked out a pair of labels for mine. The HDD fan is quiet so I leave it on most of the time. The "CPU BOOST" fan (as I've taken to calling it) is noisy so I only us it when I'm doing something like transcoding or burning loads of disks (to keep the optical drives cool)
TBH you would probably have been better off buying a bay mounting fan controller, but I like having big red doom switches on the front of my box. I may get one of them flip top switches and make a reset button.