1989 240DL K10042
Long ago in a land far away when I wasn't thinking too clearly I hooked up the orange wire (tachometer) to the back of my instrument panel (long story). Fry one electronics board attached to the speedometer. Get another one from the wrecking yard, doesn't seem to work. Try another, this time when you start the car the speedometer says I am doing 120 mph sitting in the garage (time travel). After a few seconds it drops to zero. Speedometer doesn't work nor does the odometer. The problem I have now is that I don't know if any of them works or not.

Open to suggestions.

Does anyone have a K10042 that works they want to sell?

There is very little you could have messed up other than the unit itself. It is possible that you could have cooked just this portion of your ignition switch, not probable, but possible. I had one car kick my fanny, and it was the tiny blue and copper strip, held with two screws just above the speedo. The most likely culprit is the transmitter, or the wiring to the transmitter in the rear end. For another used speedo...try www.car-part.com.