Yeah they were available in 69 and 70 fullsize cars. Had a number of those mirrors back in the day and kill for one now. They were mounted in the lower right of a standard day/night mirror, the wiring was continuously hot but separate from the courtesy circuit. The little mirror map light replaced the larger one that Buick always put on the passenger side dash. Sorry, don't have a picture of one installed.
My 1970 Skylark custom has one of those on the mirror . . . It even worked up until a few months ago!
