I have a 96' C220 with 105000 miles. This week, all at once, the speedo failed and the dash lights for the parking brake, brake wear indicator, and abs went "on". This car does not have ars or traction control. The odometer, cruise control and abs also do not work. Oddly, it even stalls when stopping whereas it did not before this speedo problem.
I checked the left front speed sensor . It had 1000 ohms resistance. I checked the dash fuses 3 and 10. I don't know it there is a separate circuit for the ABS that has a specific fuse. I took it to the MD dealer and the MD tester (100.00 tester) wouldn't work with the car . Code 100. I pulled the custer out ( it is impossible to actually get the cluster past the nonadjustable steering wheel). Who is the great Wizard of Odd out there in cyberland? Help. tryfunke

OVP or MAS relay, depening on which one you have.

The overvoltage relay has failed, causing trouble with intermittant power supply to the engine controls and leaving the speedo dead (it's electronic on that model).

Check the fuses and replace the relay (hopefully just an OVP relay, the MAS one is pretty pricey).

You can check for lack of power or voltage fluctuations to test it if you dont' want to just buy one and sway to see.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

You might check the alternator.

I was reading a Lexus board and someone had a similar problem of idiot lights triggered without any real defects. Turned out to be a faltering alternator.

glenmore
1991 300CE
1990 LS400

Dear glenmore< thank you for your reply. the alternator has now been checked and was found to be normal. I believe the mechanic said it was operating at 14.5 with a load and normal sine wave.
the ovp relay is 100.00 Is there any way to check it (out of the car) with a ohm /volt meter? tryfunke

I'm no closer to success. Any grounds to clean?

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.

Thank you very much for your reply. I have the cluster half way out and you are correct in saying the the steering wheel will have to be removed in this nontilt model car to get the cluster out completely. YOU should know I have looked at the auto parts and barns and nobles book store and have not found a manual for the c200 '96. an electrical diagram would be nice to have. How do I get one? is there one online? tyfunke

Before checking out the ground, do checkout psfreds thought on the over voltage relay etc. It sounds like an excellent guess and changing that is an easier job than trying to find a bad ground (which could be the problem but...dont know). You can check for repair CDROMs on ebay, search on your car model and look for manuals, etc. Also FastLane here may sell one from MB. Finally I think MB (the dealer) can order a printed manual for your car. On my old 1984 380sl the over voltage relay is located on the pasenger side above the fuse box behind an easy to remove panel. You might google and search here to see if someone has diy nores on where the relay is.

Those are all excellent ideas. I'll check that ovp relay location in this site. Thanks everone for your interest and guidance, it is greatly appreciated. tyrfunke

PS Philp and EricGS hit the nail on the head. Everyone really helped me to get luck on the car's problems. The problem was fixed instantly with an overvoltage protection relay. Yes, the wiring harness looks flakely in some areas that were inspected. Yes, the wiring harness may be replaced. But before replacing a two thousand dollar part, replace the ovp. Often times, people like myself don't know where it is located. It is on the passenger side (USA) near the window under a plastic cover. Ther is a fuse on top of it that In my case was not blown. thanks alot you guys tom