How do you stop condensation build in head light assembly.

Hello, The ballast is probably related to the condensation. Any contact with an HID bulb can cause hot spotting, and lead to bulb failure, but if liquid water is getting into the ballast, it will fail quickly. As for condensation, headlights can be resealed, but that is tricky for a DIY, and in the long run, it is better to replace the headlight. Cadillac will charge you quite a bit to change the headlight assembly, and parts are not cheap, but an independent shop, like those we certify, are normally much cheaper, and can use aftermarket parts that do not have the insane mark-up. Here is a list of shops in your area: http://repairpal.com/cadillac-within-10-miles-of-jeanerette-louisiana-70544