Wire tracer units aid with identifying wire runs and locations. They work very well on co-ax or twisted pair/trip wires. The tracer operates by injecting a tone into the wire(s) with the transmitter unit. The location of the wire can be found using the receiver unit. Tracers can spot the area of a wire that is located in one of numerous wire bundles or plugs.
Both transmitter test leads must be used. In the case of co-ax or twisted wires, one lead would be attached to the shielding while the other is attached to the center conductor. Isolation of the wire under test from components and ground connections is useful. I have found that using a tracer on one single conductor wire using aircraft ground as a reference for the other test lead is impossible. Anytime the receiver comes in proximity with structure, the tone will be heard (almost all wire runs are close to structure or ground). To use the tracer on a single wire requires using another wire that has a similar run. Both will indicate a tone.
Just as a note: Never use a tracer on any live wires.