Import,

My wife's 1990 740 had the same speedometr symptoms. Jumping needle all around, then eventually needle would not move at all. While getting a new muffler and tailpipe, I asked the mechanic to look at the speed sending unit in the rear differential. he said wires leaving the plug from the sensor were bare of insulation in places. A few wraps of good old black electrical tape around the wires cured the problem for us. Hope that this helps.