What would cause this?

I had the same problem one time man. What happened was that my socket that you put the bulb in went bad, and I don't know why. I had to replace it. What you need to do before checking any of that wiring stuff is to take off your front bumper, take the socket from the working side and replace the bad side socket with the good one and see if it works. If it does, then it is the socket. If it is the socket, then I know that the 92-95 model civics have the same socket that the 96-00 does. Hope that helps.