"From 2001-on, Rangers have Electronic Brake Force Distribution which is proportioning done by the ABS. Using the ABS sensors, the front to rear slip ratio is calculated in software. The line pressures are then adjusted to balance front to rear braking, driving the slip ratio toward 1.
Pre-2000 had 2 systems. RABS was standard on most Rangers, 4WABS was optional on some models, standard on others."
So it very well could be an ABS sensor. RABS was started in use on F-series trucks in 1987 apparently.
https://books.google.com/books?id=sj...ABS%3F&f=false