The speedometer on my 82' 300sd shows the wrong speed most of the time.
When car is at stop it points on about 30mph, I noticed it shows some speed (about 25-30 mph) when ignition is turned on, even before engine starts. Thee is no cables going to instrument cluster, just a wire.
How to fix?
Our reference material doesn't have any information for your vehicle. Your speedometer needs to be calibrated. This may be possible by simply turning a screw, or it may be something that can only be done at a shop.