Well i can tell from personal experience, that when i had to fix my fog lights for it to pass inspection i was laying on my back for a week trying to figure out what was wrong with it. In my case you should check underneath the fog lights, there are rubber boots that cover the opening for the fog lights ing case you need to change the bulb. What happened with mine was that water or something got into my driver side fog light housing and corroded the metal on the inside, so while my fog light was getting the positive concoction, the grounding for the light bulb was corroded so the mean't that the it was not making a complete circuit in order for it to work. So my suggestion would to be check the housing of the fogs lights and make sure the connections are all connected or making full contact and check for corrosion on the metal grounding plates or wires.