The speedometer only works part of the time. When it stops so does the fuel gage

Hello, You likely have an issue with the cluster circuit board, or the electrical wiring running to the cluster. Testing should take some time, as the error is not always present. I would recommend having a professional shop take care of the repair, if the vehicle is otherwise in good-excellent condition. Let me know if you have other questions, otherwise, here is a list of certified shops for your convenience. http://repairpal.com/mercedes-benz-within-10-miles-of-spokane-washington-99205