My wife’s 1991 740 speedometer needle sometime drops to zero and other times it shoots up to 70 mph and sticks there until you shut the car off. Other times it works fine. The odometer also doesn’t work when the speedometer isn’t working. I also just replaced the crank sensor which went out a couple of weeks ago; however, the speedometer problem was doing its thing before the crack sensor went. I have examined and cleaned the sensor and checked for loose wires behind the speedometer. I am kind of stuck on what to try next. Any help would be appreciated.