I had (have) the same problem on both my 122 adventures, and what I've used a microswitch to fix it. The switch is the depression kind, and requires very little movement to activate. You can mount one above the pedal, so when the pedal is in it's released (not braking) position, the switch is compressed and not activated. When the pedal is depressed, the switch opens and the power is sent to the brake lights. The bracket can be made yourself and the switch can be bought at an electronics store, but Ron Kwas sells a premade kit which gets rid of the hassel of trying to figure out how to mount the switch and run wiring. I'd recommend going Ron's way unless you're small enough to squeeze in between the seat and the firewall upside down to get a good look at where you're gonna make that bracket.