After attempting to install hids and failing I put my headlights back together. On the passenger side the parking light stopped working. Guessing it was a burnt out bulb I took out the bulb on the drivers side and plugged it in, Didn't work. Plugged that bulb back into the drivers side and now both font work. I checked the wires and didn't see anything loose. Anyone have a clue what's wrong?

 

It is possible you had a bad connection on the one bulb and by removing and plugging it back it you fixed the issue with the bad connection. If it's working, i'd just leave it.