Where does the speedometer get its signal from. is it mechanical or electonic?

 

It is entirely electronic. The ABS module gets the signal from the VSS (Vehicle Speed Sensor) that is mounted in the rear differential and sends it to the instrument cluster. The VSS is also used as the signal for the third (rear) ABS channel, there are also one sensor on each front wheel to drive the right front and left front channels. (The Ford ABS is only a 3 channel system.) It works similar to speedometer on a bicylce with a magnetic pickup registering when a magnet passes in front of it except in your truck, the magnetic pickup senses a "break" or open space on a tone ring attached to the rear differential carrier next to the ring. (Ring, as in ring an pinion.) You can see the electrical plug on top of the diff housing facing the front of your truck. The camshaft position sensor uses the same technology.