There is a metal rod that runs from the trans lever up to the column, actually more then just a rod, has some pivots and such (I posted pic's of this a month or two ago). This rotates a tab inside of the column that operates the back up light and ECM's P/N input switch.
Under the dash top side of column, near the firewall, white plastic piece that clips to the column. This is the switch assembly. The grease dries out and no longer makes contact. Can carefully open it for a cleaning and re-greasing. Note that it is a pain to get it back into place.
It is then adjusted by sliding part of the assembly left/right.
RemoveBeforeFlight