If you buy a new set of brake pads, one or two of the pads will probably have the wire attached (the wire can be cutoff if not needed). One end of the wire comes embedded in the brake pad so that when the pad wears down the exposed wire touches the brake disc. If the wire on the car is still there but with no connector, you would have to improvise your own connector to join it to the brake pad wire.
If the brake pads you buy don't have the wire then there is nothing you can do but I don't think this is a problem as long as the brake pad thickness is being checked say every year.
Ted