You can see if there is water inside of the control unit. Sometimes this is the case when it has a mind of its own. The control unit is under the seat. ( you can unplug it from under there as well)

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM