I need some help with this one! My 1985 300SD will not start, If I jump the starter with the key on it will run great, but when I try to start the carwith the key it will notengage the starter.I changed out the iginiton switch, vacuum lines and all but still will not start. Any advise where to look next??

 

I had something similar happen to me a couple of months ago in my 1995 C280.I was told it is the Safety Neutral Switch (somewhere under the gear shifter). I was advised that if the car doesn't start in park - to put it in neutral. Works fine for me!! Hope this is your answer.

 

check the gear selector inhibetor switch ,its attched on the selector lever,on the left side underneath the car its big plug connector with 4 pins ..............