A twin-horn arrangement was used throughout production, a high-note and a low-note horn working together to produce the characteristic two-tone sound, far more authoritative and far-carrying than a single horn. Both horns are energised by a relay activated by the horn push at the centre of the steering wheel, the relay providing the high-current switching that the horn push contacts alone cannot handle without burning. The push button switches the relay coil rather than the heavy horn current.
Specification & Fitment
Twin Lucas 9H horns became standard on all MGBs from the start of the 1970 model year, having previously been standard on export cars and home market GTs, and the same twin arrangement is used on the MGC and MGB GT V8. On the MGB the horn specification changed at chassis GHN5-417001, with two-terminal horns used on earlier cars and single-terminal horns from that point onwards, so the terminals on the existing horn should be counted before ordering. High and low note horns are available in both specifications individually, alongside the horn relay, mounting brackets, securing bolts, and all associated wiring connections. Some brackets are model-specific to suit the differing engine bay layouts.
Common Faults
Horns mounted behind the front grille or in the engine bay receive maximum exposure to road spray, salt, and moisture, and corrosion is the most common cause of horn failure, while the electromagnetic diaphragm can fatigue with age, producing a weak, distorted, or intermittent sound. A horn that sounds feeble or operates only intermittently should be replaced, as it is both an MOT requirement and a genuine safety item. The horn relay should be checked if both horns fail simultaneously, as a failed relay prevents current reaching either horn, and earthing problems at the horn brackets are a common cause of weak operation, since the bracket provides the earth connection for the horn body. Twin air horns, supplied complete with their own mounting brackets, are available for owners who want a more assertive note.