can a defective cruise control unit cause the speedo needle to bounce violently?... i mean bouncing from 5 to 85 even with the car creeping along. ..its that bad ... i checked for obvious looking kinks and seen none..

Yes, it can. I have a truck with factory cruise control (same unit as used on the cars) and the needle bounced all over too. I solved that problem on this unit by removing the gears from the cruise control unit and cleaning out all the dried black crusty lubricant from the gears and their bearings, then reassembled with a small amount of Lubriplate No. 105 grease. Problem solved. The lubricant dries up after 20 - 25 years.

On my unit the cover over the gears was held on by some hex head screws. This was the only part of the cruise unit that was assembled with screws, where the speedometer cables attach. One of the gears has the governor weights on it if I remember right. Take your time, pay attention and perhaps you can solve your problem. Also check the cable lubricant too, they can dry out and bind causing the same problem.