First off, the car wouldn't start (not even a click) and reported a 'battery/alternator' fault - applied a jump starter to the terminals, nothing. It was trailered into the main dealer and they replaced earth leads and it worked - for a day. Next day battery ran out of juice on way to work - but would restart and work with a jumper pack on the battery terminals - recovered again to main dealer. Main dealer replaced alternator - car worked, for a week. Now car refused to start - back to same symptoms as first time - about to be recovered for a third time. I'd like to replace the main dealer's strategy of randomly replacing modules at my expense until they accidentally get it right - any advice appreciated.

 

or have they even checked the condition of the battery?
find a different shop.You are dealing with morons.
You never ever jump a mercedes with cables to the battery terminals,you can fry the rolling codes right out of the drive authorization system.You always use the under the hood post and let the battery charge a bit before attempting a start.And then when started always charge over night at 10 amps till fully charged.
ohlord

 

Thanks ohlord,

You might have a point with the Morons thing ... sorry forgot to mention that when they replaced the earth leads they also replaced the battery. Voltage regulator seems to make sense; when things go wrong you get the impression that the ECU isn't receiving the correct voltage and therefore getting confused. THe last time it wouldn't start it was more like it was immobilised by the ECU rather than a lack of power from the battery.

 

They have now told me they plan to replace the 'K40 Relay' - seem to make sense? [the voltage regulator was apparently replaced along with the alternator]

 

could do it.But it still seems like they are throwing parts at it.