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MG MGA - Insulating horn on positive ground MGA

So while I was attending some other maintenance issue on my '60 MGA I noticed the right side horn was almost hanging by the wires. Turns out the plastic extension made by the PO was cracking. He had mounted this plastic plate on the bottom of the front extensions and the horn to it. There is a 1/2" bolt and a philips head small bolt in front of it holding the plate onto the frame.
So how did the original brackets insulate the horn from staying on on the positive ground cars?
Ron

See original mounting here:
http://mgaguru.com/mgtech/electric/et109a.htm

Horns are not polarity sensitive. Original Windtone horns have two wires, and neither one is grounded to the housing.

Some aftermarket horns have only one wire and use the housing as ground return. In this case the housing must be isolated from the frame of the car. The original harness has two wires, one always hot to power the horn(s) and the other returning to ground through the dash mounted push switch.

Alternative to electrically isolating the housing of a one-wire horn is to use a relay to switch input power. See here:
http://mgaguru.com/mgtech/electric/et208.htm
Barney Gaylord

Thanks Barney, ok so that's the problem. He used non original horns that ground to the outer body and then needed to isolate them on a positive ground car. So I'll order a set of the proper horns and mount them in the correct position.
Ron

This thread was discussed on 26/04/2011

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