1997 Ford Explorer Antilocks activate at low speed

Look for cobwebs and rust flakes falling onto the sensor area at each wheel. When cars sit for more than a few days, all sorts of critters can get into places they don't belong. Spiders and bees are a couple of major offenders. Also, rust flakes form in the ventilation slots in the middle of the rotor that can start falling into strange places once the car is driven again.