I don't actually own a 406, I own a 206 GTi180. However I recently what i believe is a 406 Rear view mirror that auto dims.
Looks like this
Not my car, but the mirror is identical

However I wired it up, tested it by holding my finger over the rear sensor on the mirror.
And noticed that only the central part of the mirror dims?
Has anyone experienced this, or know of any fixes at all?
I appreciate all of your help.
Thanks.