I have 2008 F250 5.4L automatic supercab. I have an issue with a couple things. The speedometer will jump around when the vehicle is not moving. Sometimes it happens immediately when I turn on the key and sometimes it will jump once when I start the engine. Generally when it jumps around a lot after just turning the key on the red brake light will also stay on along with the ABS light. I have done a lot of pinpoint checks and found nothing wrong so far. One thing I did notice was that if I disconnect one front ABS sensor, it can be either side, the speedometer does not move when starting or just turning on the key. I do not know why the front sensors have any impact on the speedometer since the VSS on the rear diff is the speed input. I have done a test rotating the front wheels to prove out the front ABS sensors and they are fine. I have checked voltage to the sensors and it is fine. Anyone out there with any thoughts on this?? The speedometer seems to operate fine when I start driving.

I have the Mitchel wiring diagram and I see the Yellow Blue wire going from the ABS VSS pin to the PCM VSS pin. There is a splice (S130) that shows a takeoff to the 4x4 module and to the wiper motor. I have no idea why there would be any connection to the wiper motor. Is there anyone out there that can explain that one?