I know it belongs in the 3 forum but all the action is here so please forgive me.

The check control on an '88 325 displays the brake lights warning even though all the brake lights are working and have the correct 21w bulbs.
The high stop light also functions and has the correct 5w lamp. I've exchanged bulbs anyway, again with the correct ones but to no avail.
Since the brake lights work the switch is good so what else?
Anyone seen this before and know the cure?
Thanks