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Horn won't turn off

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DSVW Dennis S
Ellicott city, MD, USA   USA
Hi,

I am new to this Website but not to MGs. I owned a 1968 Midget back in 1988 but it has been a long time since I have worked on one.

I recently purchased a 1972 MGB GT. The horn would not work at all. I checked each horn and am getting 12v to each unit. I decided to take the horns out, clean all of the contacts and make sure that the body metal the horn itself was attached to is good and clean for a good ground.

Now when I attach the horns to their position on the body, they go off and do not stop until I take them off ground. Any ideas on why this would be happening. I don't have a manual yet but I was thinking a relay, or possibly the steering wheel? It looks like it could be an aftermarket MG wheel.
Was hoping for advice before I start taking apart the steering wheel.

Thanks in advance!
Dennis

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chris Avatar
chris Platinum Member Chris Roop
Pendleton, OR, USA   USA
Any number of things; wiring to horn button rubbing, steering column bushings worn allowing contact, etc. Look to the steering wheel/column area. Start by pulling the horn push off and checking it.



Edited 1 time(s). Last edit at 2018-03-12 09:00 AM by chris.


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Gerry Avatar
Gerry Gold Member Gerry Masterman
Prairieville, LA, USA   USA
Your horn works by grounding the circuit downstream of the horns themselves through your horn button. This means that you should have power at the horns all the time and that somewhere downstream of the horn your wire is getting grounded. The first thing I'd do is pull the horn button off and pull the spring loaded pencil out. I'd then hook power back to the horns. If they still blow then you have a wiring issue. If they don't then you have a horn button issue. Be real sure that both horns are hooked up the same way. BTW, some horns work just backwards-they only see voltage when the horn button is pushed and are grounded internally. These horns only have a single wiring connection. You need to be sure of what you have as MGBs have used both types.

andy1965MGB Avatar
andy1965MGB Silver Member Andy Lincoln
San Diego, CA, USA   USA
1965 MG MGB "Blue Jay"
1967 MG MGB GT "Cardinal"
x2 what Gerry said.

The RH horn is the first one served by the loom, the LH (drivers side in US) is slaved to it. I would disconnect the LH horn and solve the problem for the RH one first: just in case the problem is caused by wires running between them. You can also hook up a 12V test lamp (or a turn signal bulb, etc) instead of the horn to save your nerves as you debug.

Make sure you didn't ground the horn contacts to the horn body. The two contacts on each horn are supposed to be isolated from the horn body. You can test that by an ohm meter or by hooking up only +12V, resting the horn on a cloth and probing with a ground jumper.

The horn button should ground the horns when pushed. Once you get it all working, you might consider a relay (search MGE or look in Rick Astley's book) as the excessive length of the ground wire and corrosion often makes the horns a bit weak. but first things first.

Good luck,
Andy

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danthefitman Avatar
danthefitman Dan H
Portland, OR, USA   USA
1979 MG MGB MkIII "Simply, A Great B!"
Okay, that was your horn I heard in the distance!



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gofastandfalldown Avatar
gofastandfalldown Glen Horne
Edmonton, AB, Canada   CAN
1970 MG MGB MkII "Miss Pandora Moneypit"
Something is not right. You say that the horns sound when you connect them to the chassis. That shouldn't happen and if you solve that problem, then you've solved the bigger problem.

How many connections on each horn? One or two? Should be two. Possibly these are not the factory original horns and someone has modified the wiring.

Gerry Avatar
Gerry Gold Member Gerry Masterman
Prairieville, LA, USA   USA
That tends to say that the horns have become internally grounded. Both the supply and ground connections should be isolated from ground. There should be plactic isolating washers where the connectors go through the horn body. Perhaps the one on the ground side is broken or missing?

If you pull the purple/black wire off both horns do they still sound? If they do then the problem in internal to the horns themselves

DSVW Dennis S
Ellicott city, MD, USA   USA
Thank you all.

My problem is, I think, two-fold. Both horns are working and both have 12v going to them.

#2 - In an effort to make sure all of my grounds were clean I cleaned and took my Dremel to lightly clear away paint that was built up. I don't think there was any ground because they were so painted over.

#1 - I mistakenly grounded out the wire to the horn body by adding metal washers. Thanks for letting me know that is a no-no.

The horns are now bolted up to their holders and are no longer blowing. They don't work at all now. I think the problem is in the steering wheel, horn button. I'll have a look at it tonight.

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DSVW Dennis S
Ellicott city, MD, USA   USA
BTW, my horns both have two connectors going to each.

chris Avatar
chris Platinum Member Chris Roop
Pendleton, OR, USA   USA
Horns usually have an H or an L stamped on them. One should have two terminals so you can bridge wire to the second horn which should have one terminal. I thought that the horn grounded through the body mount, but may have my makes mixed up.


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DSVW Dennis S
Ellicott city, MD, USA   USA
Here is what I have at the steering wheel in photos. Shouldn't there be a wire attached to the clip behind the horn button? Thought I would ask before I start ripping apart the steering wheel and cover. Thanks.

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DSVW Dennis S
Ellicott city, MD, USA   USA
I think I am missing my horn brush. There is a hole, that you can't see because of the shadow in the photo. The hole is located at 7 o'clock on the wheel. There is actually an old horn brush in my center console that looks damaged. I just bought the car so it must have been damaged and the po took it out.
I will buy a new one and stick it in there, hopefully that will fix it.

oleanderjoe Avatar
oleanderjoe Gold Member Joseph Baba
Fresno, CA, USA   USA
WELL That type of steering wheel and Horn Button, If I remember right, is spring loaded in the center, and makes contact with the three metal clips that hold it in to the opening. I don't think you need a horn brush. Lots of different set-ups. Any instruction sheets around for the wheel. ??????


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DSVW Dennis S
Ellicott city, MD, USA   USA
The button does have a spring like feel to it. When I push it in without the horn brush it springs back into place. More investigation tomorrow.

oleanderjoe Avatar
oleanderjoe Gold Member Joseph Baba
Fresno, CA, USA   USA
Dennis. Now I remember, the one I worked on had a spring steel clip under the center button. The black clip, 4oclock position is pushed down by the center button, making contact with the brass lug in the center. The center lug I believe is attached to the purple. Wire that normally went to the horn ring. I had a problem with the horns on all the time when the center piece was put in place. The brass center terminal, touched the steering shaft. Horns blew. You can push in on the 3 little side plastic tabs and the center piece will pop out. Is is supposed to be. “Purple wire to brass terminal, Black spring steel clip, to wheel hub, to steering shaft.” Cheers


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