Good afternoon all. Jim has made an important point that the horn is connected to a positive supply and dropped to earth via the horn push. I have seen conflicting circuit diagrams for this where the horn is earthed and receives a positive supply via the button.
I have been restoring Ruby horn/indicator units for some time but would like to source some thicker 4 core multi cables than those readily available and would advocated the fitting of a relay.
Regards
Stuart

Location: Staffordshire, the creative county.

Hi Stuart,
in theory you will always have a permanent feed from the NON earth side direct to the horn and the earth going to the horn push which completes the circuit when pressed.
So dependent on the year of the car, it's possible to have a circuit where the car is negative earth having a permanent positive feed to the horn itself and a negative feed via the horn push to a negative earthed car.

Equally, again dependent on the year the change was made in production, you can have a car whereby the opposite applies and have a car with a permanent negative feed to one side of the horn and a positive feed via the horn push to a positive earthed car.

I believe the main changeover from negative to positive earth with 'our' cars was circa 1936.

Regards Steve V.

Location: Polegate, East Sussex, United Kingdom

Thanks everyone for your input. It does seem to be a voltage drop problem, because when I take the Rist off the car and put some jump leads to it, it blares like a good 'un. Fitted to the car it just won't go. I've decided that I will rewire the lot, with a relay to switch the main current. That should do the trick. The horn wire up the column is a pretty hefty one so that should be OK. Have tried a jump lead direct to battery earth terminal and the back of the horn quadrant and it makes no difference so I guess the column is properly earthed.

Just need to sort myself a relay and some decent wire.

Happy days! I'd be dead bored if I didn't have something to mess about with.