Horn Button Grounding
Triumph TR4/4A
Intermittent horn operation can usually be traced to a defective ground circuit on the steering column. This model employs a ground circuit that utilizes the metal steering column tube to complete the circuit.
As there are two (2) flexible rubber coupling’s between the upper column section and the steering rack (the column grounding point), a low amperage “braided” ground strap bridges the insulating flexible coupling and can be seen running through the center of the rubber joint. These ground straps have a very short life and will fracture due to flexing. This will interrupt the ground circuit and intermittent contact of the braided strap results in intermittent horn operation. A further problem is the failure to refit the steering rack grounding strap during steering rack removal, (this connects the rack thrust button housing to the chassis and provides the lower ground connection).
A permanent fix for this problem is to provide a ground source above the upper flex joint. A simple method is to attach one end of a 1/4″ spring steel strap, (such as found on ignition contacts), to the body panel adjacent to the brake cylinder and have the unsecured end riding on the inner column just above the flex joint. In effect, this is a commutator brush.
There is also a potential for an open ground circuit to exist in the steering collapse/height adjustment feature that can be found immediately adjacent to the bottom of the outer steering column tube, (this can be seen to the between the battery case and bulkhead). It can be identified by a large locking nut securing an
“Allen” grub screw. Rust can cause a ground interruption at the point where the two inner column shafts connect. This problem can usually be corrected by removing the locknut and “Allen” screw and refitting. Follow factory repair manual recommendations for
reassembly.
When undertaking any work of this nature, check that the horn commutator brush in the steering wheel hub to ensure that it does not have a broken internal connection. At the same time, service the horn button by disassembling and cleaning the button contacts.