off you will need to replace the switch located at the base of the lever.
Although it doesn't seem to be a very important part you will find that the car will beep
continuously at you as you drive to alert you the handbrake is still on. Annoying.
Accessing The Switch
This can be easy or hard. Easy on the fortwo, hard on the Roadster.
Slide both seats all the way forwards, open the boot and lift up the carpet as if you were going to access the engine. With the main part lifted, push the carpet up and back until it touches the backs of the seats. You should now be able to see the base of the handbrake.
Remove both seats and subframes and get in the car. Grasp the carpet and pull it into the cabin area, fold it over on itself and you should be able to see the switch.
Replacing The Switch