Dodge Repair: 2005 ram wheel bearings, front wheel bearings, rear wheel speed

Question
I own a 2005 dodge ram 1500 2 wheel drive with 5.7 liter engine. Upon replacing the front wheel bearings noticed on left side a wire coming from the bearing. well now the auto part store is reordering me two wheel bearings with this wire saying both sides should of had this wire to begin with.
my question is, should I look and see about this wire on the rear as well? Also what exactly is the purpose of this wire? Thank you William Edom

Answer
The wire which goes to the left front bearing is actually a wheel speed sensor. The input from this sensor is used by the ABS controller to monitor wheel speed. Don't bother looking for similar wires on the rear wheels, they are not there. The rear wheel speed is measured by a sensor in the center of rear end housing.