Step 1: Create a new document in Photoshop around 200px by 200px in size.  Create a total of three layers - the background on the bottom, a wires layer in the middle, and clips layer on top.  Fill the background with white, but leave the other two layers transparent.   Now create your own clips or other relevant objects in the clips layer.  I'm not going to cover how to do that here (its a wires tutorial after all), but you can make your own quite quickly anyway.

Step 2: Now select the Pen tool and create two points at the start and end of the wire you would like to create.  No wire is this straight, of course, so we'll take some time adding a little bendiness.

Step 3: Using the Add Anchor Point tool, add a few points in the middle of the line.  Don't use too many. If you are using paths for the first time, best start out with one point only, see how it works, and build on it from there.    Now choose the Direct Select tool and play around with the anchor points to get the bendiness you require.  This isn't as easy as it  sounds, but persevere and you will be rewarded.

Step 4: When your path is just how you want it, you need to complete it using the Pen tool.  To do this, click on one of the two points you made in step 2 and connect it to the other via an indirect route.  Try and put these new points as far away from the curvy bit as you can - you'll see why very soon!

Step 5: Go to the paths palette and right click on your new path.  Choose Make Selection and, if your version of Photoshop has these functions, a feather of 0, but with anti-aliasing ON. Press OK.  Now go back to the layers palette and make the wires layer active. Select Edit > Stroke from the menu and stroke a path 8px in width with a colour of your choosing.  I opted for #FF0000.   You can now delete the path if you like.  If your new wire is very jaggy, try running through my anti-aliasing tutorial with a Gaussian blur of 5 to smooth it out.

Step 6: Now all you have to do is grab the eraser tool and delete the bits you don't want.  A few seconds of work and you should end up with something like my example on the left.

Step 7: Nearly there!  Just select Layer > Layer Style > Bevel and Emboss from the menu, with the wires layer still active, and enter the settings shown here.  Then press OK and look at your nice new 3D wire!  

Step 8: You shouldn't stop there of course.  Feel free to add drop shadows to everything, a funky background, or even patterned stripes to the wire using pattern overlays (accessible from Layer Styles).    Just experiment and soon you'll be creating the coolest wires and cables known to man.  :)