Mercedes: colling fan speed controller, fan speed controller, fuse holder

Question
was wondering if you could  tell me  where  the  fan speed controller   earth lead is  connected  i  have had a problem with   my ecu  and i  have been told it   is more than likely   caused by a  bad earth

Many Thanks Brian Davies

Answer
Brian, not knowing the year model, I will just guess this vehicle has some age on it.  Grounds become a problem with age as the joints develop corrode. I would begin with the fuse holder, particularly if this vehicle uses ceramic/aluminum bullet fuse. Locate the fan fuse and clean the joints and replace the fuse with copper strip type.
Make sure all the electrical ground straps are cleaned and tight. Also make sure that the battery terminals are cleaned and lubricated and tight.
Good Luck
Robert