Engine not starting or Starter not Cranking?
Mercedes or not the Starter Battery stuff is mostly the same as other Cars.
If you have an Automatic Transmission there is a Neutral Safety Switch that can go bad your Starter will not crank.
You can try starting in neutral to see if it works there.
Worn Shifter Bushing can cause a similar problem.
If the Starter is not cranking try a jumper wire from a Posative source to the small terminal on the Starter Solenoid. If it cranks like that you have some issue between the Starter, Neutral Safety Switch and the Ignition Switch.
Bosch or Beru Glow PLugs are the only ones that hold up well. I tried Autolite Glow Plugs and barely got 2 of them out of the Cylinder Head due to the tips becomming swollen.
When the Glow Plugs were out the holes should have been reamed out with a Glow Plug Reamer made for the job or some alternative method.
I believe if there is enough Carbon around the Glow Plugs the heat goes into the Cylinder Head and the Coolant instead of heating up the Air in the Precombustion Chamber.
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