The ABS sensor harness connector joins the wheel speed sensor wire to the body harness. Because it sits inside the wheel well, it is exposed to water, mud, and road salt. The plug uses rubber seals to keep moisture out. If the seal fails, corrosion will rot the pins, cutting the sensor signal.
If your ABS light comes on after driving through deep water, a wet connector is a likely suspect. Unplugging the connector, spraying it with contact cleaner, and applying dielectric grease often fixes the issue.