A 220v outlet for a dryer has 3 or 4 wires depending on its age. The normal colors are white, green, black, and red. If there are only three they will be green, white, and either black or red.With four wires the black and red both go to the hot sides of your service(one to each leg!). The white will go to your neutral and the green will go to the ground. In a 3 wire system the black(or red) wire goes to one leg. The white goes to the other leg (these are the two you have connected if your dryer is working) The third wire (it should be green) should go to your ground. A nearby cold water pipe (before the shutoff if possible) will work as a nice ground if you don't have a grounding rod or loop. It will work without the ground but it's not considered safe. REMEMBER TO DISCONNECT THE POWER SOURCE BEFORE MESSING WITHE THE WIRES.
