I hesitated to respond to your first post because I don't own your particular car, but my first thought was a bad ground behind the instrument cluster. I had a similar set of issues on my car, isolated to one part of the instrument cluster (temp gauge, fuel guage, turn signal). If you have checked everything that everyone else here suggested (a few folks like psfred on the relays are quite experienced from what I see), then you should check for a bad ground behind the instrument cluster. You probably need to get that steering wheel off on your car, there are a number of posts on that. Look at the electrical diagram for your car (the MB documentation) and see if there is a common ground for the items that failed in your instrument cluster. I found that on my issue. Then you may need to go back there and run a NEW ground to another part of the car from where it was previously grounded. As these cars age, the electronics seem to become more sensitive (resistance and impedence of components changes over time) and I think they become more sensitive to noise in the ground. This is just a guess on my part.