Well I attempted to post this in the DIY Section but would not allow me for some reason so I'll post it here. Driving home the other day I got caught in heavy rain and had left the cover off the back of the head light so in turn the ballast had gotten wet. I thought I was going to have to buy another, but i tried to dry it myself after it sat for a day.
First of all you can access the ballast from the wheel well and is probably the easiest. You will need a short phillips head screw driver to get the ballast out. Here you can see the ballast hangin once you unscrew all three screws.
Next unplug the main power supply, unscrew the screw next to the bulb power supply, and unplug.
Then you should be able to remove the ballast and take the three screws holding the housing together.
Once you get the three screws out you might have to use a flat head to gently pry it apart.
when you got it apart it should look like this.
My ballast was full of water and you could here it swish around inside when you would shake it.
First use a vacuum and suck out all the excess water. This prevents the water from getting further into the circuits. Then use a towel to soak up the excess water and moisture. Finally you can get a hair dryer and dry up what ever seems to be still wet. Be careful to not get anything too hot, because you can warp the circuit board and accelerate corrosion. Once finished go back and plug your ballast back in, cross your fingers and hope you just saved yourself a trip to the stealership. Hope this helps some.