Ran into this problem with a 1999 R1100gs, it was the brake light switch. I'm not sure if the 1100 and the 1150 share the same front master cylinder or not, but the brake light switch on the 1100 sits just below and attached to the master cylinder. Over the years, brake fluil had leaked out of the master cylinder bowl and onto the switch. It ate away at the switch until one day, no brake light. Replaced the switch light worked again.