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MG MGB Technical - Horn electrical problems

I decided to try to fix, rather that replace my non-working horns on my 77 MGB. I removed both horns and bench tested them. The high tone horn worked fine on the bench and works fine by itself, when activated in the car from the turn signal stalk.

I disassembled the low tone horn and cleaned the contacts. Now it works great on the bench with test leads and a hot battery. However, when installed in the car, neither will work. I only get a single odd tone for less than a second, then nothing from either horn. Any ideas will be appreciated.
Bob Duke
RW Duke

Bob - Check all of the wiring (especially the connectors) between the horns and the horn push and between the horns and the source of power. It sounds like you have a bad (high resistance) connection somewhere. Good luck - Dave
David DuBois

With a voltmeter connected between each horn terminal and ground operate the horn push. Ideally you will get the same 12v on the purple all the time, and 12v dropping to 0v (ground) on the purple/black. If the 12v on the purple drops when the button is pushed you have a bad connection going back through the fusebox to the brown. If the purple black doesn't drop to 0v you have a bad connection going back through the horn push and column to ground. Mine were the same and I fitted a relay as there were several causes of volt-drops in the purple/black circuit, the biggest being inside the MotaLita horn push.
Paul Hunt

This thread was discussed on 08/09/2003

MG MGB Technical index

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