Helping a friend ..speedo is not working and without some understanding of how it gets its signal i can't help. Does the wheel speed sensors report to the traction control module which then sents an analog signal to the speedo? I have a broken 2 conductor wire exiting the hood at the drivers side and a matching wire that goes into the fire wall possibly to the speedo...Not sure.but the onl other wire exiting the hood on the passenger side is in fact a 2 conductor but the wires are different colors and the loom/sheathing is much different than the wires leaving the drivers door...I realize this may seem a jumbled mess but if any one could set me straight i'd appreciate it

There if a fuse in what is called a coffin box on the passenger side of the engine bay. You have too take the lid off with four TORX bolts holding the lid down. Once the bolts and the lid is removed, you will see 4 10 amp fuses. I believe the second one in from the left is blown. Go ahead and replace it. This should fix your problem.

The wheel sensors do send signals to the cluster for the speedo. It could also be the ASR module in the coffin box..

This is bang on. Just went through it myself! Had the car parked over winter in the garage, and drained the battery. Made the mistake of boosting it from one of my other vehicles. Shouldn't have done it as I learned. As a result, my speedo stopped working. One of my buddies is a tech at the Mercedes dealership. Took it there on a Saturday, he hooked it up to diagnose it. Same place where the plug for the diagnostic tool plugs into, are the fuses that are mentioned above. You got to unbolt the cover to access them. Of course one was blown. So we replaced it, and speedo started working. The only problem after that, which I was not able to take care off so far is the MPG indicator. Since that incident it started working again, but now backwards for some reason