The E class for a start!
Most newish mercedes have some kind of electrical issues and they are notorious for these problems
Source What car:
USED Mercedes E-Class (02-06)
What should I look for?
Above all, look out for problems with the electrical systems, especially on early cars. Mercedes prides itself on being first with advanced electronic gizmos, but this car had problems.
Prod and push every switch to ensure they work. And, if the car has an automatic gearbox, make sure that it changes gear as it should, that the engine idles smoothly and there are no flat spots when accelerating.
On every model, also check that all the warning lights come on when you turn the igintion on, and then go out when the engine fires. Note also that the battery can go flat if a car is left for as little as three days (some owners fitted an upgraded battery to counter this), the electronics governing the brakes can go haywire, leaving the system in ‘limp-home’ mode, and the paintwork on older cars can scratch too easily or even flake off.
Overall, the car received a kicking from owners reporting to the JD Power customer satisfaction survey, while the What Car Reliability Index shows plenty of faults, too.
TRADE VIEW
"Great car spoilt by electrical reliability concerns"
John Owen
Buyer, Fords of Winsford
http://www.whatcar.co.uk/used-car-look-for.aspx?RT=2294&type=5