momunaf

hi,folks please help..i have been trying to solve this problem for a while.i have 1997 mercedes e300 diesel.this is my problem i have check engine light on and the code is p0600 all the lights will come on once in a while when driving ets brake lining speedo meter will drop to zero and the transmission will not shift from low gear.i have read the forums few folks had the same problem.to replace the k40 relay which i did and the problem went away.so i decided to drive to LAS VEGAS after driving about 600 miles bam the light came on again.now some times at a light stop the engine will stall and when i try to start it the glow light will not come on as soon as the glow plug light come's on it will start.now l'm thinking will the k40 relay gone bad again l was also advised by a mechanic that the instrument cluster is bad.please help if you had this problem thanks a millon.