I have two wooden posts in my backyard and there is an outlet box located on each post that is controlled by a single switch in my house. I removed the outlet box from the first post to install a light instead. I found two wires running into the outlet box. I capped off one of the wires and connected the second wire to the new light. However, the light does not work and, also, the outlet on the second post doesn't work now either. My guess is that I need to somehow connect the capped-off wire to complete the circuit but I'm unsure what I should do with it.

By wires I take it that you mean cables. A wire is a single wire, a cable is two or more wires in an outer covering. Each cable should have a black and a white wire. Connect the two black wires together and add a "pigtail". A pigtail is a short piece of wire. Connect the two white wires together and add a pigtail. Connect the light to the pigtails. This should be a GFCI circuit or the remaining outlet should be a GFI outlet.

Thank you for the information. I hooked everything up this afternoon and it works perfectly. Much appreciated.