Morris Minor Owners Club

Let me start by saying I am a Member of the Institute of Electrical Engineers, but NOT a Vehicle Electrician so I need some help on this baffling problem.
The horn used to work but it failed the MOT as it somehow stopped working. When I disconnect the horn and measure voltage I have 12v between positive and earth. When I put a continuity tester on the other wire, I get a circuit to earth when I push the horn button.
When I measure voltage between the two horn wires I get 12v when the button is pushed.
I have tested the horn and it toots when I put 12v across it, but just to be sure I spent 26 quid yesterday on a new horn but it still won't toot.
If I connect the horn onto the live wire and connect the other cable to earth, it doesn't toot.
This is driving me up the wall, I'm considering taking it to an auto lecky to sort out as I've run out of ideas.
I should point out we are now negative earth.
Ideas anyone?

Sounds like there's resistance in the fuse (or its contacts) that drives the horn. It should be the one with purple wire one side and brown the other. I'd give its contacts a good clean and if that doesn't help then replace the fuse - the fuse wire in glass fuses can fatigue over time.

The horn takes a good few amps so any resistance upstream would give a significant voltage drop to the horns terminals.

Alex

Great idea, I'll check it now, which fuse is it?

Alex,

You're a star, just popped out, saw which fuse it was and tested by holding the "fused" wire to the live side and TOOT TOOT. So I cleaned the fuse and the contacts, plugged it back in and TOOT TOOT.

Thank you so much.

Cheers
Tim

Hi Tim,

Good to hear you've fixed it! I'm in the middle of designing an F1 chassis loom, so your's was easy

Cheers,

Alex