what causes moisture in headlights?

Answer 1

condensation
a cracked housing
bad seal around the bulb holder

any one of these could be the culprit

Answer 2

The short answer is: moisture is entering from a failed seal.

Long answer: if your headlight is a large, glass, all enclosed item (called a sealed beam type) then any number of reasons are to be had. The inside of these lamps are in a near vacuum, and even the tiniest of leaks in the seal will allow moisture to be drawn in. A small rock chip in the lens area can also be a source of the moisture. The only fix to these is to replace the whole headlight.

If your headlight lamp is a small, removable bulb that can be replaced without having to remove the entire fixture, then again, a failure at the seal is where you want to look. Sometimes the bulb can become loose in it's socket, and allow a gap to form in the seal letting in the moisture. The fix is to remove the entire headlight fixture, remove the moisture from the housing, and make sure of a good seal where the lamp mounts into the fixture. A new bulb may be necessary, especially if you touch the glass part, or find that the seal has failed.

Hope this helps. :-)

Answer 3

I assume you mean in the lamp housing.... if it is not sealed properly it will collect moisture from the air and when the headlights are on the inside area becomes very hot... and then cools off allowing moisture/condensate to form on the inside....

Answer 4

It can be the slightest crack, or the seal. You probably wouldn't be able to see it. It could even be the seal from where the bulb fits in to the back.

Answer 5

Water.

ADDED:
I'm just kidding.
Usualy it's a bad seal at the back of the light housing where the light bulb holder screws in.
Or a cracked housing....

Answer 6

Drill a small hole in the bottom corner an the heat will dry it out.