I've just finished installing an BMW OEM rack off a later model bike to our March 2000 K1200LT.
After lining up the rack by eye the support legs were marked out on masking tape with a pencil, next I applied some of the other half's almost fully used (saved from the bin) lipstick to the bottom of the legs. Then applied the rack to the marked out masking tape, which left a perfect template to drill the 6.5mm holes vertically into the top cover. A further hole of 14mm was marked and drilled centrally under the front rail to facilitate the high level brake light wiring to the inside of the top cover. The rack was then attached by using the supplied 6mm x 30mm Allen head Fillister bolts and original spacers.
According to the technical documentation the electrical connectors and wiring were not fitted to models before July 2000 after which the connector is fitted behind the lower cover of the vanity mirror.
After removing the interior light cover and a little tugging on the wiring loom I discovered two cables taped to the light cables which were the correct colours for the brake light circuit. (Grey/yellow trace (+) & brown (-)).
These were joined using insulated cable connectors to the chopped off existing connector. (Purple (+) & orange (-). The vanity mirror & light were refitted, the box closed. All ready to go.
Regards Sparky