The issues with th VW don't suprise me at all. However Mercedes doens't seem to have a history of electrical issues except a bad run of wire harnesses that had bad insulation. Nothing like a BMW wiring nightmare!

Any way Merc systems may be a bit involved and sometime complacated.
there systems have a lot of protection such as relays for most everything meaning most of the wires have low curent and just the relay to the component hast higher curent. The problems you mentioned are likely to be caused by the relay itself sense its intermitant. and the heat thing well the climacontrol assembly thats another mater.