This recent thread discusses that ABS Valve, even though the subject is Master Cylinder Diameter.
It also includes
this link about testing one.I didn't scour the thread for another link but I believe there was one more in there someplace. Subject RV was a 1993, and I don't know if the chassis was 1993, could have been earlier.
Always work from the CHASSIS year (dashboard VIN and Ford/Chevy door jamb label) and NOT the year Fleetwood or whomever called your RV.
ABS diagnostics, at least on these Fords was NOT part of the OBD-1 suite. Even finding the connector, which I believe is underhood near the brake booster, would not read out the ABS Codes. There was a gyration to get the ABS Light to blink them out. I think something in the above links steers you to that process.
