I may have found the problem causing headlight condensation. Some time ago I got some condensation in the passenger side headlight. Somewhere I found a post about people pulling headlights, drying them out, and putting desiccant bags in them. Another post said there was a TSB about improperly assembled headlights. There are three vents at the rear of the headlight that are designed to let the heat from the headlight drive the moisture out and some were assembled with the protective caps on so tight that the moisture couldn't escape.
After thinking about it I decided against the desiccant. If moisture is getting in and not getting out, you will ultimately get condensation no matter how much desiccant you put in. So I just dried mine out, made sure the vents were correct, and reinstalled them. I got more condensation.
Thinking maybe I didn't get all the moisture out I tried again. This time I made sure there was no more water in the unit. But I damaged the yellow lens on the side by letting the unit get too hot from the hair drier I was using. It didn't matter how hot I got it; I still got more condensation in the unit.
One more try....I pulled it again (I'm getting pretty good at this now). This time I pressurized the unit with a vacuum cleaner and doused it with soapy water at every seam and joint. No bubbles. So the only place for moisture to get in is the vents or, wait for it, the back cover which I pulled off to dry and pressurize the unit.
I used some butyl tape, the kind used to bed glass in windows, and added it on top of the gasket on the back cover. It has only been two days, but before I had condensation the next day, and I have no evidence of condensation.
So if you have condensation in a headlight, pull it out, remove the vent caps, remove the back cover, hold the unit horizontally as it would be in the car and rotate it backwards to allow any liquid water to drain out the opening in the back. Hook up a vacuum cleaner with the hose on the output of the cleaner instead of the input or use a hair dryer on a LOW setting and let it run for several hours. Check it periodically to ensure it doesn't get too hot. When dry, let it cool down and reassemble it. Put the vent caps on so they just stay in place. Do not push them until you can't push them any more. Get some butyl tape from a window place and use it as an additional seal on the rear cover. Then cross your fingers and hope it works. That's much cheaper than a new light.
Al
After thinking about it I decided against the desiccant. If moisture is getting in and not getting out, you will ultimately get condensation no matter how much desiccant you put in. So I just dried mine out, made sure the vents were correct, and reinstalled them. I got more condensation.
Thinking maybe I didn't get all the moisture out I tried again. This time I made sure there was no more water in the unit. But I damaged the yellow lens on the side by letting the unit get too hot from the hair drier I was using. It didn't matter how hot I got it; I still got more condensation in the unit.
One more try....I pulled it again (I'm getting pretty good at this now). This time I pressurized the unit with a vacuum cleaner and doused it with soapy water at every seam and joint. No bubbles. So the only place for moisture to get in is the vents or, wait for it, the back cover which I pulled off to dry and pressurize the unit.
I used some butyl tape, the kind used to bed glass in windows, and added it on top of the gasket on the back cover. It has only been two days, but before I had condensation the next day, and I have no evidence of condensation.
So if you have condensation in a headlight, pull it out, remove the vent caps, remove the back cover, hold the unit horizontally as it would be in the car and rotate it backwards to allow any liquid water to drain out the opening in the back. Hook up a vacuum cleaner with the hose on the output of the cleaner instead of the input or use a hair dryer on a LOW setting and let it run for several hours. Check it periodically to ensure it doesn't get too hot. When dry, let it cool down and reassemble it. Put the vent caps on so they just stay in place. Do not push them until you can't push them any more. Get some butyl tape from a window place and use it as an additional seal on the rear cover. Then cross your fingers and hope it works. That's much cheaper than a new light.
Al