06 Since our Ram has antilock brakes, we need to reuse the tone ring. The tone ring is part of the ABS, and is a gear-like ring that mounts to the differential—under the ring gear, and measures the speed of the vehicle’s wheels. Inside the rear end case is a wheel sensor. The sensor is a permanent magnet with a coil around it. This is a magnetic pickup that senses the individual teeth on the tone ring. As each tooth passes under the sensor, it trips the magnetic field. This creates a single-direction current in the coil windings inside the sensor. The voltage signal then travels to the ABS control module. This is how brake pressure is modulated so the wheels will not skid.