If I remember correctly the purpose of the trailer converter is for when the tow vehicle has two seperate systems for stop lights and turn sigs (seperate bulbs). The box takes those signals and allows the single bulbed trailer light to flash when you have the brake lights activated. I suspect if you are trying to combine a two light set up into a single bulb light fixture you have something wired wrong. You say "second bulb" is there more than one bulb in the new fixtures? Kind of hard to help trouble shoot with out seeing and knowing exactly what you have and how you are trying to wire it.
