hi, i'll be happy to help you in anyway i can.
good news, it may be as simple as a bad brake lite switch.
Ok, so how do I check it to make sure?
it's cheap, i would just replace it.
Where is it? Is it the one that is actuated by the pedal? The brake lights are working, would it still be the problem? Do you have a part number?
sorry no part #, and yes its on the backside of the pedal assembly. most 2001 mercedes used the same one.
brake lites are a seperated circuit.
replace it you should be good to go.