When you say the engine does not start, what is the symptom exactly?
1. Does the engine crank(meaning; does it turn and does not start),
2. OR does it do nothing( does not turn at all)?
This is where the path of diagnosis can go in two different directions:
1. If it cranks and does not turn, then the problem is related with spark to the plugs, fuel to the cylinders, or poor compression. The fact that the problem is intermittent, this would eliminate poor compression—just about. If we have no fuel, and/or no spark, the cause could be related to just about anything; a faulty sensor/s, wiring, poor electrical connection, control modules, fuel pump…on and on. I am not saying it’s all these things. We will have to diagnose the problem.
2. If the engine does not crank at all, then this issue is related to a faulty battery, starter, no power to the starter….etc. and somewhere along these lines.
In any case a faulty battery can cause all sorts of issues on this vehicle. Including lighting and radio issues.
Having said that: The issue with your headlights could be a faulty control unit, and or sensor/s. The lighting module may even need a re-flash.
The issue with the radio, again could be; faulty control module, radio or even a re-flash.
Very important to realize that this vehicle is very sophisticated and full of electronic control modules, it really has a mind of its own. The shop/technician that works on it has to have the proper diagnostic equipment that has full capabilities and not an aftermarket diagnostics scanner. We have the O.E.M. Mercedes diagnostic equipment and the expertise to diagnose any problem with this vehicle.
If there are issues, the control modules store fault codes in memory. We will need to perform a scan on all the modules and see if there are any current and/or stored faults and go from there.
I hope this helps a little…