F-150 Speedometer, etc

My 1995 F-150 4WD's speedometer flops around. The PU also stutters at stop signs. The cruise control is unusable because the speedometer flops. My mechanic replaced a sensor on the rear axle, but it only cure 1/2 the problem, so he put the old sensor back in. He said there must be a short somewhere. Any other ideas on what may be my problem? Thanks

Sounds to me like a Wheel speed senor problem. I would check for a good reference voltage from the computer, then check the ground circuit( on both left and right sensors.) If these are good check the sensor itself with an ac voltmeter. It should produce a voltage if not replace the sensor. I hope this helps you

you should have a speed sensor at the back of the tranny, thats the one I would check first. the one in the rear end and on the front wheels should be for the abs.