Could also have a short due to worn insulation on a wire. I use a seat belt warning buzzer to check for electric power, instead of a test light. I pirated it from a past car before it went to the bone yard. Add some wire and gator clips, you can hear if you have power. I would start at the lights, and see if you get power at the bulb sockets, if not follow trace the wire back and keep checking till you have power. I doubt there is a problem with the ground if the other lights are working. It has to be in that circuit someplace.