My 83'Turbo 300D cruise control is inop. also my speedometer is inop. but the odometer does function correctly and records distance as accurately as possible for an 18 year old MB. My question is, does an inoperative speedometer disable the cruise control or control any of its functions. Next question is, where and what section of the Mercedes Benz CD service manual tells how to trouble shoot this problem if it even covers the subject. I have not been able to locate it.