High-intensity discharge lamps (HID) provide significantly more light than incandescent bulbs in automotive applications. One drawback to these systems is that they require the use of ballasts, which are small electronic boxes that handle the voltage needs of the HID bulb. When installing HIDs into a non-HID equipped car, figuring out where to mount the ballasts can pose a challenge to the car owner looking for a clean install.
Examine the engine bay near your stock headlights for a suitable mounting location. Ballasts should be kept dry and clean, and require (ideally) a flat mounting surface. The ballasts will be connected to your headlight bulbs, so you need to make sure the wires running to and from the ballasts will not get caught in the engine cooling fans or the engine serpentine belts. A good place to mount the ballasts is on top of your fuse box, on top of the factory air box, or on a plastic fender liner, as these locations sit high in the engine bay, and are on the sides of the motor, thus separate from the engine's belts and fans. Another good mounting location is the front cross member near the radiator.
Clean the chosen ballast location with an alcohol wipe. Assume you are using the fuse box as your location. After the plastic is cleaned and dry, lay down double-sided adhesive tape on the fuse box, and then attach the ballast to the box. Make sure you properly orient the ballast to take into account wiring before mounting, so that you avoid making hard kinks in the wiring.
Use zip ties, or drill a small hole and use self-tapping screws, to secure the ballast if you decide to mount it to a metal surface such as the front cross member, in addition to double-sided tape. Many ballasts have mounting tabs on the ends to help secure the ballast. After the ballast has been mounted, place a dab of silicone sealant over the screws to protect against rust. If you are mounting to the plastic fender line, use a small drill bit to drill holes into the fender liner, then use self-tapping screws to mount the ballast, in addition to using double-sided adhesive tape.
