This is one of those things that everyone overthinks. People are always asking, "Where does the black wire go, and where does the white wire go?" The first thing to remember is that the white wire never touches the switch. On a regular wall switch, the two gold screw lugs are just for the black wires.
Think of a switch as a gate that opens and closes. It lets electricity in when it's open and it doesn't when it closes. You attach the black wire that comes from your power source (the circuit panel) to one of the gold screws and the other black wire that runs to the light (or other device) to the other gold screw.
The white wires (and there should be two of those) are simply tied together with a wire nut. And lastly, the two ground wires are attached together to the green ground screw.
A three-way switch is not interchangeable with a regular switch. Period. You have to accept that. All to often, I have customers trying to purchase a three-way switch to replace a regular switch because the three-way looks "beefier". Trust me, if your regular switch isn't "beefy" enough for what's going on, then you have other problems.
What is a three-way switch? In a room with a ceiling light and a way to turn it on and off from two different locations, you use three-way switches. Assuming that you are replacing an existing switch and not running new wiring yourself, it's not too difficult.
When you first remove the cover plate and pull the old switch out (AFTER having turned off the breaker), you will see an extra wire in the box, usually a red one. You will also notice that there is an extra lug on the switch itself. This is where you say to yourself, "Wow, I had an extra wire and an extra place to put it. Isn't that nice." Yes, it is. It will also be nice if you haven't detached the wires from the old switch. This way, you can see exactly where the wires go.
If you've already taken the wires off of the old switch, you have a little extra work ahead of you. First, slap yourself upside the head for taking the wires off the old switch before seeing where they go on the new switch. Second, you should have three wires to deal with here (and a ground wire, more than likely), two black wires and a red wire. Or, depending on how the switches were wired, you might have two black and a red on one switch and a black, a red and a white on the other switch. It all depends on whether the two switches were wired "in-line" and then going to the light fixture, or if the wiring went from switch to light to switch.
Now, aren't you sorry that you took those wires off too early?
The one thing you can count on is there being only two wires going into the light fixture itself, and maybe a ground wire depending on the age of the fixture.
Either way, the diagram on the right should help.
Once upon a time there was a big bad wolf who was moving to a new house. He huffed and he puffed getting his washer and dryer into the moving van. Why didn't he have any help? Hello, he was a big bad wolf. Anyway, he gets to his new digs, again with the huffing and puffing, he unloads the washer and dryer. He puts them in the laundry room, hooks up the washer and then tries to hook up the dryer.
Uh-oh. The cord on his dryer doesn't fit the receptacle in the wall. Forget the huffing and puffing, now he's just ticked off.
So enough of the fairy tales. Hardly a day goes by at our store where we don't get someone needing to fix the same situation that has befallen our big bad wolf. Here's what you need to know.
There are three types of power cords or "pigtails" that are commonly found on clothes dryers (shown at right). Two of them have three "blades" and one has four blades. Of the two pigtails with three blades, one of them has an "L"-shaped blade and two straight blades and the other one has three straight blades. The pigtail with four blades has two straight blades, one "L"-shaped blade and one round blade. So when you move from one house to another, you have a 1 out of 3 chance that your old pigtail will fit at the new house.
If you have to make a change, rule number 1; NEVER TRY TO CHANGE THE RECEPTACLE IN THE WALL!
Rule 2) Turn the circuit breaker off for the dryer. After you rewire the pigtail you can turn the breaker back on after you plug the dryer into the receptacle. If you somehow mis-wired it, it will simply pop the breaker. But, if you plug a mis-wired pigtail into a receptacle that's hot... you won't be very happy.
If you are changing from one type of 3-prong plug to the other 3-prong plug, it's very simple. The three wires on these cords are laid out in a row, as opposed to a round bundle. Simply detach the wires in the access panel on the back of the dryer and attach the replacement pigtail the same way. You may be asking, "What if I have it backwards, left to right or right to left?" The answer is that it doesn't matter. the two outside wires are the "hot" leads and the middle wire is the "common". Either way will work.
Going from 3-prong to 4-prong, or 4-prong to 3-prong requires a couple of extra steps.
Going from 3-prong to 4-prong you will have an extra wire, assuming that your old pigtail was the original. In the access panel, there should be three lugs where the pigtail is attached. When you attach the 4-prong pigtail you will notice that the wires aren't in a neat little row, but that's okay because they should be color coded (if not, take it back to the store and get one that is). The red and the black wires get attached to the outside lugs and the white wire will be attached to the middle lug. Remember, the black and red wires are interchangeable. This leaves you with a green wire. Simply attach this to the frame of the dryer, easily done by using the screw that holds the access panel shut. But before you do this last step, check the middle lug where the white wire is attached. If there is a small wire running from that lug to the frame of the dryer, cut it.
Going from 4-prong to 3-prong is similar, but in reverse. Now you'll have 3 wires and 4 lugs to deal with. When pulling the old 4-wire pigtail off, note which lugs had the red and black wires attached to them. Then, when you attach the new 3-wire pigtail, simply put the two outside wires on the red and black wire lugs and the middle wire where the white wire was attached. This leaves you with an extra lug. For safety, attach an insulated wire from the white wire lug to the extra lug, and you should be good to go.
No huffing and puffing.