Ground Wire for Mercedes Benz C280 Where is it? what does it look like?

I watched a youtube video about foreign cars and why they would all of a
sudden there were temporary stall outs, and then one day the car didn't
start.  It failed.  Then came the issue of crank, no start.  I received some
valuable information here on Car Gurus and thanks for that. I also asked a
couple of mechanics. They said get a diagnostic. I did. Twice.  I was told to
replace the following: crankshaft position sensor. I did that.  I was told to
replace the spark plugs. They had all ready been replaced, just weeks
before the stall.  I was told to replace the Ignition Coils, if bad.  I found 2
were bad, so I replaced them.
  There is still NO SPARK!!
I saw one video that said it may not even be all of the above. it could be a
corroded ground wire.  I was told it was a wire on the engine, up top or
bottom.  Problem is, I don't know what that even looks like.
Can someone share with me what the ground wire on a Mercedes Benz
C280 Engine looks like.  I can't even find a diagram online.
I will check it for corrosion and maybe my problem will be solved after
cleaning off the corrosion.   Thank you!!