I got the repair kit from SNG Barrett for the horn electrical parts associated with the steering column on my 1958 2.4 Mk 1.
The kit contains a little very thin square piece of brown hard plastic about 3/4" on a side. I have the factory parts manual for 2.4 Mk 1. Plate AZ on page 283 shows all the horn electrical pieces associated with the steering column. I cannot find any part that looks like this little thin plastic square. I have no idea of where it goes on the Mk 1. Is this kit for other cars as well as the Mk 1?
The insulator is fixed sandwiched between the contact and the rubber mount. It folds over the top of the connector. It is there to stop the power for the contact shorting out and actuating the horn.
You cut the insulator into a sort of fat T shape with a hole for the screw.