brake lights stuck on 1994 730i

Hi I posted this on the 7 series forum aswell. The brake lights are stuck on most of the time and I can't trace the fault at all. The diagnostic machine says no problem present, it's not the switch, all connections are good, any ideas anyone?
Does the light control module govern this? I know that some of the front light problems can relate to a wiring harness fault but would this affect the rear brake lights? BMW have no idea what it could be which isn't that reassurring.
thanks