Cuzzo

Ok my 2011 W221 had a no crank sound problem one day..all lights come on but nothing when u turn the key. I figured it was the starter. So I took the starter out and tested it and the solenoid was bad. I tested the new one before I installed it and the new one came on.. ok I installed the new starter and purchased a new battery because the battery had died on me a week prior from trying to figure out the problem ( doors open, using scan tool) battery had a dead cell..so changed the starter and battery and still having the same problem.. no cranking sound but lights are working...need help!! What could this be?