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MG Midget and Sprite Technical - Horn stopped working

midget MkII 1965, negative earth.

The horn stopped working. I've checked the horn via a 12v supply and it works. I've checked the continuity of the wiring from the steering wheel centre button to the horn (PB) and back (P) via the fuse (not blown) to the control box (N). When I push the horn button I get 8v across the horn connections with the engine off and 12v with the engine running.

Resistance between the steering wheel centre button earth and the body appears to be very low.

I'm at a loss other than completely replacing the wiring for the horn. I suspect low current due to high resistance and that would perhaps point to a poor earth connection or wire degradation.

Where should I look for the earth connection? There's a connection on the front o/s wing that emerges from the wiring loom - would this be relevant?

Could the control box output be at fault?
P Rafferty

They dont call the wirng harness "the prince of darkness" just because it sounds cool.

But before you go ripping out the wiring you might consider removing the horn and using some jumper wires to the battrey and see if its the horn itself.

you can get aftermarket horns at any autoparts store

On my work truck I have to replace the horn every 2 years as it likes to rust up inside... so try that 1st
Pro P

is it an air horn or electric?
on air horns it is sometimes the compressor getting stuck. a little wd-40 and white lithium grease fixed mine pretty quick.
if its electric i have no idea.
Seth Brecklin

My button was not connecting to the wheel properly due to some paint on the inside of the steering wheel boss, a coulple of seconds with some wet and dry sorted it.
R Fowler

Carefully pull out the pencil and give it a good clean

It all sounds like it is working, or should be, but I would try and clean all connections and ensure any earths you find or that are indicated by the bible are getting a good earth and not just sat on rust barely making a circuit.

You seem to have answered it yourself, although I would dare say it would be connections degrading a whole lot quicker than the wiring itself.

Pete
PeterJMoore

Some horns:

http://www.vuvuzela.fm/
Adrian Jones

Am getting one from Sainsbury's as soon as - not enough people take notice of my horn at the moment!!! Now I just have to learn to blow at the same time as screaming abuse at the offender ;)
rachmacb

At one stage I thought that a parp-parp horn bolted on or the vuvuzela might just be the only solution.

However, AVO meter at the ready I checked the steering column earth by measuring the resistance to the negative terminal of the battery and concluded: a great earth.

I then re-measured the voltage across the horn terminals and found that it was a bit variable and often very low ~2-3v. This pointed to high resistance somewhere in the cabling. I'd previously checked continuity throughout but hadn't checked it with any sensitivity across the fuse.

Finally I checked the control box terminals and checked the output voltage there: +12v. Back to the A1-2 fuse and +12v on the brown side and... 2-3v on the purple side. Bingo. Sand paper on the fuse terminals and around the fuse ends. 12+v volts on the purple side.

Rewired the horn, push the button (as the Sugababes once said) and parpppppp.

Thanks for all your suggestions.
Paul Rafferty

This thread was discussed between 16/06/2010 and 17/06/2010

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