Interesting experience. Generally the ABS system is independent of the Powertrain Control Module (PCM) and not accessible by commercially available scan tools, even on today's OBD-II vehicles. In the early '90's a technician often needed either a special adapter cable to plug in to a special ABS diagnostic connector or in some cases just a test light, jumper wire, or screwdriver to turn a switch and watch an LED blink.
For the 1997 F-150 special software in a professional scan tool, or a dedicated ABS and airbag scan tool is required to access the diagnostic codes of the ABS system as well as real time sensor information.
-Rod