Help me build a Hard Disk On/Off Switch! =)

OK, I have to ask...
Why do you wish to build this?

Randomly powering off drives will very often lead to data loss.

Just checking. I've heard stranger things.

But don't just twist the wires together. If you're going to do it, do it right.

Here's is another link for making one: http://www.extremetech.com/extreme/82086-build-your-own-sata-hard-drive-switch

It outlines exactly which wires (by color) should be connected to where.
Do you have a multimeter? And you really need a soldering iron.

Do you have a switch yet? A case for this?

In lieu of this kind of makeshift workaround that's sure to cause you problems of one sort of another in the future...

Why don't you consider installing removable HDD/SSDs (mobile racks) in your desktop PC - a configuration that's tried & true and has been used by thousands of PC users over the years? By doing so you'll achieve your basic objective of isolating your drives from each other both physically & electronically and by a mere push of a ON-OFF power button immediately activate the drive of your choice on-the-fly. It's eminently practical as long as your desktop PC case has one or more 5 1/4" bays for installation of the mobile rack(s).

I prepared a broadside for my computer club with some details on the installation & use of these devices. If you're interested, so indicate.

The multimeter is to test connectivity before you apply actual power to a drive, and let the magic smoke out.

Just in case you got it wrong.
I used to fix fighter jets. Lots of electricity, data signals, etc.
This is a simple wiring job.

There is no way I would power a drive up with this without testing the basic connectivity though each switch and wire.
Just in case.

Especially if this is your first time (no soldering iron, no multimeter) building something like this.

But...as ArtPog says, there are MUCH better, easier, safer, ways to do this.

In lieu of this kind of makeshift workaround that's sure to cause you problems of one sort of another in the future...

Why don't you consider installing removable HDD/SSDs (mobile racks) in your desktop PC - a configuration that's tried & true and has been used by thousands of PC users over the years? By doing so you'll achieve your basic objective of isolating your drives from each other both physically & electronically and by a mere push of a ON-OFF power button immediately activate the drive of your choice on-the-fly. It's eminently practical as long as your desktop PC case has one or more 5 1/4" bays for installation of the mobile rack(s).

I prepared a broadside for my computer club with some details on the installation & use of these devices. If you're interested, so indicate.

5.25 drive mount. Accessible from the OUTSIDE. No case opening needed after you install it.
Take a drive out, put a new drive in
Boot

http://www.amazon.com/StarTech-com-5-25in-Trayless-Mobile-3-5in/dp/B000KS8S9W



12v or 5v? You need to wire it for that specific drive.
I don't know which ones you have. But if a particular drive requires 12v, then that is what it needs.

No problem...(I can sense your frustration).

But there is a viable solution for your objectives...

The remarkable thing about the mobile rack I'm going to tell you about is that you would need only a SINGLE vacant 5 1/4" bay on your desktop PC. That is because a removable tray (caddy) is used to make up the removable HDD/SSD configuration. So you could utilize a hundred different drives should you desire with a single mobile rack and insert/remove each in your running system as long as your motherboard supports "hot-swapping" - which virtually every modern motherboard on the market supports today.

Here's the general description of the mobile rack (removable drives) configuration I prepared for out computer club.

We equip every PC we build with at least one mobile rack/removable HDD/SSD. The advantages of this configuration are enormous as I will explain.

Here's the mobile rack we've been using for quite a number of years...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

1. The beauty of installing removable HDD/SSDs in a desktop PC is that the user can easily work with multiple installed drives, each effectively isolated (when desired) from any other installed drive. Thus, multiple operating systems may be installed on different drives installed in the system and no conflicts will arise from this situation since each drive can be completely isolated from another. In addition, the use of removable drives facilitates accommodating different storage/backup needs that the user may desire since it's a simple matter to add, remove, modify a HDD/SSD using a removable drive in the system.

2. With removable HDD/SSDs desktop PC users have an UNLIMITED number of drives to work with should they choose without the need for opening their computer cases to install (or remove) the drive in the machine. Again, each removable drive is isolated from the other internally-connected drives at the user's option.

3. Assuming the drive in the mobile rack contains an OS, simply by pressing its power switch the user can thus boot to this drive or that drive without the need for any "bootloader" or any other multi-booting software, as well as avoiding the need (in most cases) to access the motherboard's BIOS to change the boot priority order in order to boot to this or that particular HDD that contains a different OS.

4. Should a removable HDD/SSD become defective/dysfunctional that needs to be removed & replaced in the system, it's a simple & quick process for a user to remove & replace it from the comfort of his or her computer chair without the need of disconnecting/uninstalling the disk from the motherboard's internal SATA connector.

The mobile rack we use is a two-piece affair - a removable tray and the rack itself which is affixed to the desktop PC's 5 1/4" bay (identical to affixing an optical drive or some such 5 1/4" device). This model contains a small fan that is dead silent in operation.

This particular mobile rack model is equipped with an ON-OFF power switch button, a most desirable feature in our opinion. Assuming a user is working with multiple removable hard drives in their mobile racks (or has also installed a fixed internally-connected hard drive), it's a simple matter to press the ON-OFF button and "on-the-fly" temporarily disable one or more of the mobile rack's hard drives without the need of using the rack's lever to remove the rack's tray (caddy) containing the HDD from the rack's internal SATA power/data connectors.

Of course should the user choose to do so it's a relatively simple matter to press the removable tray's lever release button and thus physically disconnect the removable tray containing the tray's HDD/SSD SATA data/power connectors from the mobile rack's connectors. A simple pull of the tray's lever is all that is necessary.

So can you see the advantages in your situation? In effect, you would be able to electrically connect or disconnect your 2 TB HDD from the OS's internal system by a simple push of the rack's power button. Should you desire to physically remove the HDD from the system all that would be necessary is a pull on the removable tray's lever and out would come the removable tray with the installed HDD.

And should you desire to use additional HDDs for one reason or another, simply remove the present disk from the tray and plop a different one in. Thus, you would have an UNLIMITED number of drives at your disposal.

So with a removable HDD, you get the speed advantages of an internally-connected drive when you need it and the absolute security of the backup/storage data on that disk by easily disconnecting/uninstalling the disk from the system whenever you need to.

A 2 drive hotswap bay? Yes, they make those.
For the 2.5" drive, you get a 2.5"->3.5" adapter plate. It then fits into a standard 3.5" space.

Are there? You can research as easily as I can.