What would cause vehicle light cookie to change position when switching vehicles?

I may have asked this before but I'm unable to find the post if so.

What would cause the light to jump to a different location when switching vehicles?

This is what I'm referring to, the "cookie":

 

I suppose. Everything was working fine until I changed something, it broke, I reverted back to the files that worked before but still nothing. I did have it happen before but I can't remember exactly what broke it or how I fixed it.