I am not sure if they have the proper diagnostic equipment, but Redlands Truck Service found my problem and fixed it. (Contamination on the sensor.) Not in Arizona, but relatively close. The light is no longer on. And yes, it does light during the startup, so they didn't just disconnect it!!
In 5+ years I have never hit the brakes hard enough to trigger the ABS system, so don't ask me if the system works.
Another repair shop did state that the ABS system is probably not necessary under most conditions. You are not likely to lock the wheels. But in rain, snow, or other slick conditions it could be pretty important.
'04 Alpine Coach 36' MDDS