i had this probelm with my aftermarket headlights and basically i took em back off dried them out real good, make sure ur gaskets around the lights are sealing properly and also on mine there were two little drain ports on the corner lenses and i put tape on the port to keep it from "fogging", u might could use some cleat rtv silicone to go around the part of the light were it is bonded together, hope this helps
i had that problem with the little corner on the 01 headlight. I removed the entire headlight and drilled a 1/2" hole on the underside. I chose a spot that would not have water forced into it by driving in the rain yet allows the light to breathe and release humidity. Works great. As for the headlight, you can try this on the back side. on the bottom of course.