For the driver's side I mounted it on my cold-air intake box. Had it not been there I would have mounted it on the fender well next to the headlight. On the passenger side I mounted it on top of my windshield washer fluid box. I used some industrial-strength velcro I got from work to hold them on. Just make sure you clean the surface you apply it to first. Yeah deciding where to mount the ballasts was the hardest part.

where did you mount your ballasts for the hids?