The RABS unit should have given a code. This is not normal. Here is a snapshot of where the said module is located. Just for others who come on this thread.
I know this is an old thread, but I would like to know how the conclusion to change this module came about.
There MUST have been a code. The unit would have surely set a body code or a chassis code. Anytime a ABS light is active, the unit records an event.
Now as Nickd said, probably a bad solder joint in said unit. Not uncommon, since these rangers were a mix of mazda and detroit.
I did fix one of these problems, again as Nickd said, with bad pin connections. However, there was a code. The scanner gave me a no communication code and I went from there and traced the wires until I was able to determine the client NEEDED a new module. Indeed, the pin connections needed resoldering, and it was later resovled AGAIN because some idiot replaced the radio with some walmart crap and in the process while tapping into the live wire for sound, caused an intermitent with the RABS module.
All sensors where sound, and unit when tried on another truck gave the same code. It was a no communication code which needed diagnosis pronto. In 1999, the ABS or RABS unit was intigrated to the bus line and OBD protocal.
So, I will just say it again, do not want to be an as$hole, but there MUST have been a code to come to this conclusion.