I want to know how to add a new light to an existing light switch? There doesn't look like there is enough room in the box to add any new wires, and I don't want to over load it. How many lights can you run off one switch?

Well you don't normally add a light directly to a switch. You add a light to an already existing light. The number of wires in a box is limited to the size o f the box and the size of the wires (as well as other things). Tell us more about what you want to do. Maybe we can help.