Speedometer Stopped - '86' 420SEL

It seems like I fix one thing on this car, then something else falls apart. This morning while on the highway, my speedometer just stopped! What an awful feeling. (I'd just passed a parked state trooper.) Can somebody tell me why the miles continue to turnover, but the speedometer does absolutely nothing. Is this common for this model at this age? Also, anybody got a clue as to how much this will set me back? What parts will I need to make this repair? Thanks!

Just a question:

Was this car sitting for a while or under very limited use before you bought it? If so, I had a similar problem with a 'sitting' '86 SEC about 3 years ago. Upon my early driving/usage, several fuses - which were old and brittle - began failing.

So - try to check the fuses first. It MIGHT be this simple.
In you fuse box (which is at the top-rear of the engine compartment, just in front of the driver--big black box) is a removable card with description of fuses, functions, placement, etc. Check that first. If not the problem, then you will have to have a tech look at it.

Good luck.

All fuses are new and have been rechecked. The previous owner alleges that this car had been in use and not just sitting. I'm not sure about allot of things this guy told me about this car and it's care. All other gauges in the dashboard are working just fine. The speedometer remains on "0", when I drive it. Could something have wiggled apart? If so, what? Is this job a DIY?