installing a 12v one wire horn

S

steve31

Junior Member
I have a one wire 12 volt horn and have not been able to determine how/where the one wire from the horn gets connected to the wires in the harness--vehicle is a 1931 which has been converted to 12v, but did not have a horn. Any insight would be appreciated. Thanks.
 
One Wire? You may have to investigate inside the horn. The original horns had a "hot" feed to them, and the steering column button provided the ground path through a second wire. Even if your vehicle has been converted to 12V-, there should be a "hot" feed to the horn with a resistor or rewound armature (12V), and a lead to the light switch area which is the ground through the button in the middle of the wheel. If you actually have a one-wire horn, it is internally grounded to it's own frame, and will not work with the stock horn button unless you rewire the horn. Modern cars provide a "hot" from the horn switch, Model A's have the horn button provide a ground path to an already 'hot' horn, irrespective of voltage or +,- polarity.

I'm sure somebody here can post an "A" wiring diagram for you.
 
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All modern horns have one wire. They are grounded when attached and have a pos wire going to them thru a relay . check your every day modern store bought car you drive
 
To answer the man's question: you hook it up with a horn relay. The horn gets its ground through the mounting stud/nut. You supply 12 volts to it with a relay.

The relay is wired up so that it is looking for a ground (ground seeking). That is the wire you connect to the wiring harness for the horn button to provide the ground when you want the horn to blow. You feed 12 volts directly into the relay to power both the relay (when horn button is pressed) and to power the horn itself.

Do not get a relay that is grounded by the mounting bracket. Get one with a ground pin that a wire connects to.

HTH.
 
wiring-diagramcolor2sm.jpg
 
Thanks for the direction--I will make sure the relay I have is the proper one. Where does the relay get mounted/connected and what do I do with the second wire coming out of the harness through the conduit at the horn--I want it to look reasonably good? I appreciate the input!
 
Steve31, You do not need a relay if you can open up the horn and find the internal wire that goes from the motor to ground. Simply disconnect it from the horn frame (ground) and run it out as the second wire. Take a look at the diagram posted by Mike V.
 
steve31 said:
Thanks for the direction--I will make sure the relay I have is the proper one. Where does the relay get mounted/connected and what do I do with the second wire coming out of the harness through the conduit at the horn--I want it to look reasonably good? I appreciate the input!
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That solid yellow wire is the power source for the relay and the horn.

You can mount the relay inside the frame rail on the drivers side, up close to the radiator. Keep it dry. Hope that helps.
 
I compared the diagram Mike posted above and the one on fordgarage website and I see no difference. Can you tell us where the difference is? Thanks Bill G
 
MikeK said:
Steve31, You do not need a relay if you can open up the horn and find the internal wire that goes from the motor to ground. Simply disconnect it from the horn frame (ground) and run it out as the second wire. Take a look at the diagram posted by Mike V.
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This would be the easiest way to wire it as close to the original way and not use a relay.

If you can't easily get inside the motor to disconnect the ground wire, then you could insulate the horn mounting bracket from ground and run the case to the ground wire (wire running to the horn button).
 
Sorry to ask again, but I still do not have this solved. Without using a relay, I connected the one wire from the horn to the yellow wire on the harness, added a ground wire to the horn and connected that to the blue/yellow wire in the harness--without mounting on the stud, the horn blew well when the horn button was pressed. Believing that I had solved it, I then mounted the horn and reconnected the wires, however now the horn blows constantly, even without pressing the horn button. I then disconnected my added ground, thinking that mounting already provdes a ground now, but the horn still blows constantly. I have not been able to find the ground wire in the horn to disconnect (from a suggestion above offered earlier). The instructions for the horn relay switch I have (Mac's #A13802HR) seem to imply a 2 wire horn (6V?), so do I need the other horn relay (Mac's #2Q-13853), or something I can obtain locally? I am no electrician, but I seem to be making this more difficult than it should be! Please offer a solution so I can move on to something more satisyfing! Thanks.
 
While it really is simple,what your problem is takes a long time to explain.The harness is meant for a two wire horn.The original horn has juice in it all the time,and grounds and blows when the button is pressed.The button just grounds the whole thing.With a one wire horn,the horn grounds through the mount,and is meant to blow when power is put to it.It is meant to have power sent down to it to blow,the opposite of what the original A does.A one wire horn is really not meant to be used with an A circuit,but if you can isolate the ground you can make it work.Myself I don't trust those old cheapo JC Whitney type horns that so many bought.I really don't know how to make a simpler description,but if you can get how it works then I can complicate it with using a relay.
 
The simplest thing would be to buy some insulating washers and insulate the horn mount from ground, then run the horn button wire to the horn mount.

What Mike K. said about getting inside the motor and finding the ground wire and disconnecting it from ground and connecting it to the horn wire is the second easiest way to use your horn.

You can also use a relay, but that involves more work and money.
 
I am reasonably sure it is an aftermarket horn--it has no markings anywhere and the "horn" portion seems a bit flatter than how originals appear. Also, the hole in the round "sleeve" was much too small for the proper conduit to fit, so I enlarged that to be able to insert conduit.
 
steve31 said:
I am reasonably sure it is an aftermarket horn--it has no markings anywhere and the "horn" portion seems a bit flatter than how originals appear. Also, the hole in the round "sleeve" was much too small for the proper conduit to fit, so I enlarged that to be able to insert conduit.
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All right so forget about finding the ground wire in the horn. You need a relay to do it right. You may get away with insulating it but there is a lot of vibration to wear through the insulator.
 
Stick with the relay because heavy amperage through the horn button will cause arcing at the button that will eventually stop it from working.
 
I wouldn't worry about the relay right off,I believe in using them for anything with a real draw,but first you need to get an understanding of what you have,how it works,and get it working.Then wire in your relay.A one wire horn is just not an original horn,and the harness is not wired to run it as it is.Horn relays are needed on later cars because they have an endless contact at the steering wheel end to make contact while the wheel is turning.A very fragile and easy to burn out contact point.The A contacts are fixed,the button just grounds when you push it,with no turning at the contact points.If all your contacts are good an A horn will work fine for years with no relay.I have seen relays used as a band-aid measure in A's,if they had just fixed their problems they would not need them.I am remembering all the cars I would get ready for inspection back in the 70's.We installed dozens of buttons under the dashes of cars because the contacts were burned under the steering wheels.The wiring was easy to open up,and the buttons were 50 cents.
 
While I appreciate the comments and ideas, what I really need is a specific suggestion or recommended solution, such as: you need to obtain_____________, then install it thus_____________, in this order____________. If I need to be more specific as to the situation, please let me know. Thanks for your help!:o
 
steve31 said:
While I appreciate the comments and ideas, what I really need is a specific suggestion or recommended solution, such as: you need to obtain_____________, then install it thus_____________, in this order____________. If I need to be more specific as to the situation, please let me know. Thanks for your help!:o
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If you can't make heads nor tails from all the suggested methods above, take the horn to an electric motor shop and tell them "This 6V DC motor driven horn has an internal connection grounding one motor lead to the frame. Please locate and disconnect that internal connection and bring it out as a separate, second lead". Then connect it as a stock model A horn.
 
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