After going through the adventure of changing the gearbox to a lower mileage replacement only to discover that the actual problem was a water-logged TCU (but at least our forTwo now has a gearbox with significantly fewer miles on it and a new clutch), I have now moved on to the brake pedal switch (S9/1, in the service manual).
Before the gearbox problem started, it turns out that the car was occasionally showing signs of the brake pedal switch failing, specifically, the side of the switch that is connected to the ESP control unit (N47-5 in the service manual). For those of you who haven't looked at this, the switch has one circuit that closes when the pedal is pressed which goes to the SAM (N10/10) to turn on the brake lights and another circuit that closes when the pedal is not pressed which goes to the ESP.
Between when I replaced the TCU and started doing test drives to confirm it works and now, the ESP side of the switch went from work OK, failing intermittently (requiring using the MBII to clear the code before the car could be shifted out of Park), to failing constantly (so I had to use the hidden, yellow switch before the car could shift out of Park).
As near as I can tell, there are three versions of brake pedal switch which can be identified by their color, the brown one, the white one, and the blue one. The first two are "adjustable" and the last one is "self-adjusting". For pictures of the brown and white ones disassembled, see Fixing a faulty brake light switch
. The adjustment is the transition between closing one circuit versus the other. The service manual that I have came from after the switch to the self-adjusting switch, so does not describe the adjusting procedure.
If you look back in the posts for these forums, you will see that I (under my old, original account AlanPerry) posted about a brake pedal switch problem that our forTwo was having and that it made a couple trips to the dealer on the back of a flatbed to get fixed. On our car, it seemed to take some effort to get the switch adjusted correctly after the first one was replaced. The one that I removed from our car was a white one.
The brake pedal switch is under the floor. It is accessed by dropping the front underside panel. It is designed to be opened with the car on a lift. If can be opened with just the front of the car lifted, but it isn't ideal to do it that way. The dropped panel is in the way of most of the good places to put jack stands. The panel is held in by a bunch of screws with 10mm heads and one 10mm plastic nut. There is an interior panel held in by two more 10mm plastic nuts that makes access easier if it is removed as well.
If you order the OEM part for the brake pedal switch (Stoplamp Switch, 451-545-02-09-28), you get the switch and the cover (for weather protection) for the bottom of the brake assembly under the floor. The Mercedes parts diagram is confusing. The part number for just the switch is listed as discontinued and the parts diagram for the part number above just shows the cover even though it includes the switch as well.