<E28> speedo bouncing, then nothing

[PeterSchop@xxxxxxx]

Hey, what happened to my speedometer?  When I drove to work this morning it 
worked fine. I got in the car a few hours later and it started to  bounce up 
and down like it was on a spring. It would go from about the speed I was 
driving to zero then back. This lasted for about two miles then dropped to 
zero and stayed there. 

Now I have no speedometer, trip/odometer and the average speed on the 
computer stopped working also. When I tried to reset the average speed on the 
computer, it just went to 0.0 and stayed there. I drove about 25 miles and 
the range stayed at 245 the whole time although the average MPG started to 
drop a little after resetting the average speed.

Now what still works.  The tachometer, temp gauge and the fuel gage is still 
at a little over half tank. The batteries in the SI board went dead over two 
years ago which hasn't caused much of a problem.

What should I look for to fix the speedo? 

Peter Schoppelry
528E   stuck at 183,662 miles 

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