Certain embodiments described herein are directed to couplers configured to provide an electrical connection between two or more separate electrical wires. The boring tool and the cable transmit a boring tool locating signal and a cable locating signal, respectively. The LEDs are provided in closed-loop arrangements on the surface of the probing head and said means for picking up the re-emitted radiation are arranged at the centre of the rings formed by the LEDs that emit radiations whose respective emission spectra are contiguous.