The Ford ABS wheel speed sensor is one of the developments in safety being placed on cars to help the driver control their vehicle better in slippery and inclement conditions. There are usually four of the ABS wheel speed sensors on your Ford; one for each wheel. Each of them has to be functioning properly for the ABS system to work as it was designed to operate. To help the driver know if this safety system is operating as designed, there is a dash light when the ABS wheel speed sensors are being tested. Once all of the ABS wheel speed sensors pass the test, the ABS light on the dash will turn off. If one or more of the Ford ABS wheel speed sensors are faulty or just not sending a signal, the light will remain on warning the driver of this condition. The danger of just one of the ABS wheel speed sensors malfunctioning is that wheel could lock up and the computer not be aware of it causes the driver to lose control of the vehicle. The problem on your Ford could be as simple as mud, snow or debris has covered the end of the sensor so it cannot make its designated reading on the wheel's speed. It could also be damaged from debris from the road since it is under your Ford vehicle. A rock could also damage the wires cause a break in the sensor line. Any or all of these could keep your ABS light in your dash on warning you of a problem. The testing of an ABS wheel speed sensor requires an ohm meter set on resistance. Locate and unplug the sensor on your car or truck and test the two contacts. If there is little to no resistance, then the sensor is faulty.