I have one Xenon headlamp that has not worked for months. I actually changed by lamp (at considerable expense), but that was not the problem. It worked intermittently for some time, but now not at all. My mechanic told me I needed an igniter, but when I did a search all I came up with is a controller. I figured they were the same thing, but when I read previous posts, I see that they appear to be different parts of the light assemblage. Can I get one without the other, or are they usually sold together?