If I where to buy a shift light does it tell me when to downshift.

 

Not that I know of. You basically set it to illuminate at a specified RPM. It doesn't indicate which way to shift. If you set it at say 4000 RPM it will flash every time you hit that mark. What you do with that info is up to you.

Go to the photo gallery. A member recently posted pictures of his install. He may be able to give you a better answer.