The wiring harness mercedes uses nowadays in general sucks; it is not only a C280 problem. The Sprinter vans in Europe suffer a lot from shorts due to the bad isolation tape mercedes uses nowadays and it is not uncommon to see these vans in a burned out appearance...
The wiring harness are all the wires and cables from front to rear connected to all possible electrical equipment. I have had the complete wire harness of a C36 AMG pealed out to install a lot of electrical parts in my C250D and I must say that the wire harness in the C-class is not anything close to descend. Mercedes is saving money by putting in inferior wire harnesses...
When you have trouble with the wire harness you will notice it; the symptoms will become VERY clear... (malfunctioning of any possible electrical equipment). As long as you don't have any problem; there is nothing to worry about...
with a minor 600+k