I know that C280s are infamous for their dying wiring harnesses. What exactly is the wiring harness? What is it's function? Where is it located? How do you know when it's bad? what are the symptoms? What causes it to go bad? Also, is it true that most MB dealers will replace them under the goodwill mercedes policy? Or is it worth notifying MBUSA to get it replaced?

The wiring harness is the central nervous system of your vehicle. It is bundled in a protective sleeve that is slit down the middle and is routed along side the driverside of the valve cover. First clue to look for is the water temp. sensor above the thermostat. If the two leads have split insulation and the copper conductor is visible then you have indication that the wiring harness is showing signs that it will need to be replaced.IF the insulation is cracked open or split very gently use your nail ot a small flat tip screw driver and gently try to open the split of the insulation. IF the insulation cracks or a piece falls off then the insulation has become very brittle. Cause? could be high under hood temps. and or poor quality insulation, or a QC issue with the original batch during manufacture, or combination of all. Have your MB tech give it a going over it is a issue that he should be well versed in.
As far as replacement the dealer in Houston said that they will work with each one on a goodwill basis. IF you bought an extened warranty as I did the dealer said that they will NOT use the MB goodwill but rather let the extended warranty pay for it all.
My tech here in Houston mentions it as a walk-in procedure, drop the car off and pick her up the next day, no big deal. 'cept fer the cost if it's a goodwill issue with MB.
Hope this helps, course could be all those high 'G' turns slinging the molecular structure of the insulation over to one side and exposing the conductors he-he jest kidding :D :D
Keep between the lines and under the Red Line! LH

Hottee,

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...

greetingz,