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So, we have power to the relay. But no power out, to the brush. I would suspect the relay if all wiring to the relay is correct and not swapped anywhere.
The relay has the blue-yellow wire from the turn signal switch, the yellow- green is 12v and the black goes to the horns themselves. I am guessing the relay acts as a switch and connects the blue-yellow and the black to complete the ground path. Wiring not my strong suit.
It's a standard three post relay . Power comes in and goes to a flexible post and a winding around a steel post. If ground is applied to the other end of the winding it turns the steel post magnetic , pulling the flexible post to make contact with the horn post. If you're winding is broken it will never provide magnetic field to activate the horn... Exception is if the winding wire is contacting the case, and you provide 12v from the ground end.
Last edited by FarmMotorSports; Oct 14, 2025 at 07:49 PM.
It's a standard three post relay . Power comes in and goes to a flexible post and a winding around a steel post. If ground is applied to the other end of the winding it the steel post magnetic , pulling the flexible post to make contact with the horn post. If you're winding is broken it will never provide magnetic field to activate the horn... Exception is if the winding wire is contacting the case, and you provide 12v from the ground end.
Thanks I will try replacing the relay. It can't hurt
Now if there is 12v provided from the relay to the brush wire... But no 12v at the brush, you get to find the broken wire or contact point. Firewall plug? Column plug? Wire to the lower brush? Lower brush? Wheel contact? Upper brush? And I'm sure there is more!
The ground path goes from the battery negative to the frame. The steering gear is connected to the frame, so the ground passes through it and then across the jumper wire at the rag joint (not usually a jumper wire, but it should suffice) to the steering column flange. From there, it continues to the tip of the steering column where the nut holds the steering wheel on.
When a person presses the horn button, it makes contact with the tip of the steering column, connecting it to the top brush, then to the contact plate, and finally to the lower brush. The lower brush sits in an insulated plastic socket that’s part of the turn signal switch, connecting it to the blue-yellow wire. From there, the blue-yellow wire travels to the firewall connector, then to the engine side, and finally to the relay center connector. The blue-yellow wire is labeled #1 in the wiring diagram.
The 12V positive comes from the battery post to the solenoid and then to the relay connector as wire #33.
The horn-side ground comes from where the horn is bolted to the radiator support, which in turn should be bolted to the frame—completing the chassis ground path. The frame is the common ground, often referred to as chassis ground.
Without the horn button in play, there can’t be a complete path, so no current flows. The ground path would not show any 12V potential. If you try to hook 12V from the relay connector to the blue-yellow wire with the horn button installed and pressed down and everything else correct, you’ll create an immediate short to ground. That wire will begin to heat up quickly—too long and you’ll “let the smoke out of the wire,” which is technician shorthand for catastrophic failure.
However, if the horn is not in place, you should be able to measure a 12V potential at the brush. Since there’s no current flow, this simply confirms continuity from the horn brush to the relay ground connector on the blue-yellow wire. It’s the same test as checking continuity from the horn brush to the relay connector.
With the connector attached to the relay, there is a constant 12V potential coming to the relay. But the ground path is not typically complete because the horn button spring holds the button up, preventing contact with the tip of the steering column. “12V potential” means it’s possible to measure 12V, but with no current flow, it’s not doing any work.
Think of a 12V battery sitting on the garage floor, connected to nothing. You can measure 12V across its terminals, but since there’s no completed path between them—other than the meter, which has very high internal resistance—no current flows and the battery does no work. If you place a crescent wrench across the terminals, you’ll create a direct short. The wrench will fuse to the terminals, sparks will fly, and the battery will now be doing work—welding the wrench to itself. The meter would still read 12V, but now current is flowing and energy is being expended.
The relay can be tested out of circuit by grounding both the housing bracket and the terminal that the blue-yellow wire would normally connect to. Then apply 12V to the terminal where the yellow-green wire usually connects. With your meter touching the relay housing and the terminal that the black wire typically connects to, you should see a 12V reading. This is again just a potential, since the black wire terminal isn’t connected to the horn, which would provide a path to ground through the horn’s mounting bolt to the radiator support.
Technically, in electrical circuits, conventional current flows from positive to negative—even though electron flow is actually from negative to positive. It doesn’t really matter how you visualize it, as long as you understand that current doesn’t flow until a circuit is completed.
The same 12V going to the relay on the yellow-green wire (the low-current side) is also used on the high-current side going to the horns. The high-current side ground is provided by the relay housing being grounded to the inner fender. The low-current side ground is provided to the relay via the blue-yellow wire, but only when the horn button is pressed—using the ground path coming up the steering column as described earlier.
If the battery is hooked up normally and you can seat the relay connector enough to establish contact with the yellow-green and black wires, then grounding the terminal that the blue-yellow wire normally connects to should cause the horn to sound. This tests both the relay and the horn. It also confirms that everything is sitting in a ready state, just waiting for the low-side ground path to be completed. The high side doesn’t change when the horn sounds—other than the internal contacts being energized by the low side, which closes the relay and completes the high-current circuit to the horn.
The ground path goes from the battery negative to the frame. The steering gear is connected to the frame, so the ground passes through it and then across the jumper wire at the rag joint (not usually a jumper wire, but it should suffice) to the steering column flange. From there, it continues to the tip of the steering column where the nut holds the steering wheel on.
When a person presses the horn button, it makes contact with the tip of the steering column, connecting it to the top brush, then to the contact plate, and finally to the lower brush. The lower brush sits in an insulated plastic socket that’s part of the turn signal switch, connecting it to the blue-yellow wire. From there, the blue-yellow wire travels to the firewall connector, then to the engine side, and finally to the relay center connector. The blue-yellow wire is labeled #1 in the wiring diagram.
The 12V positive comes from the battery post to the solenoid and then to the relay connector as wire #33.
The horn-side ground comes from where the horn is bolted to the radiator support, which in turn should be bolted to the frame—completing the chassis ground path. The frame is the common ground, often referred to as chassis ground.
Without the horn button in play, there can’t be a complete path, so no current flows. The ground path would not show any 12V potential. If you try to hook 12V from the relay connector to the blue-yellow wire with the horn button installed and pressed down and everything else correct, you’ll create an immediate short to ground. That wire will begin to heat up quickly—too long and you’ll “let the smoke out of the wire,” which is technician shorthand for catastrophic failure.
However, if the horn is not in place, you should be able to measure a 12V potential at the brush. Since there’s no current flow, this simply confirms continuity from the horn brush to the relay ground connector on the blue-yellow wire. It’s the same test as checking continuity from the horn brush to the relay connector.
With the connector attached to the relay, there is a constant 12V potential coming to the relay. But the ground path is not typically complete because the horn button spring holds the button up, preventing contact with the tip of the steering column. “12V potential” means it’s possible to measure 12V, but with no current flow, it’s not doing any work.
Think of a 12V battery sitting on the garage floor, connected to nothing. You can measure 12V across its terminals, but since there’s no completed path between them—other than the meter, which has very high internal resistance—no current flows and the battery does no work. If you place a crescent wrench across the terminals, you’ll create a direct short. The wrench will fuse to the terminals, sparks will fly, and the battery will now be doing work—welding the wrench to itself. The meter would still read 12V, but now current is flowing and energy is being expended.
The relay can be tested out of circuit by grounding both the housing bracket and the terminal that the blue-yellow wire would normally connect to. Then apply 12V to the terminal where the yellow-green wire usually connects. With your meter touching the relay housing and the terminal that the black wire typically connects to, you should see a 12V reading. This is again just a potential, since the black wire terminal isn’t connected to the horn, which would provide a path to ground through the horn’s mounting bolt to the radiator support.
Technically, in electrical circuits, conventional current flows from positive to negative—even though electron flow is actually from negative to positive. It doesn’t really matter how you visualize it, as long as you understand that current doesn’t flow until a circuit is completed.
The same 12V going to the relay on the yellow-green wire (the low-current side) is also used on the high-current side going to the horns. The high-current side ground is provided by the relay housing being grounded to the inner fender. The low-current side ground is provided to the relay via the blue-yellow wire, but only when the horn button is pressed—using the ground path coming up the steering column as described earlier.
If the battery is hooked up normally and you can seat the relay connector enough to establish contact with the yellow-green and black wires, then grounding the terminal that the blue-yellow wire normally connects to should cause the horn to sound. This tests both the relay and the horn. It also confirms that everything is sitting in a ready state, just waiting for the low-side ground path to be completed. The high side doesn’t change when the horn sounds—other than the internal contacts being energized by the low side, which closes the relay and completes the high-current circuit to the horn.
Thank you. That is awesome info. You really are a scholar and a gentleman for being one step away from crazy. (:
I just did this YouTube video which may help although my audio seems to have been too low on my phone, so I'll re-record it later, but I need to dash to an appointment right now. Black and yellow are grounds. I didn't have any black jumper wires with alligator clips, so I used yellow to substitute. Red is hot 12V throughout. The push button represents the horn button.
I thought my recording volume was too low but it sounded fine on my phone and not on my computer - after looking at if for a minute I recalled my computer speakers also have their own round control **** on the one speaker to turn them off/on and volume up/down so once I turned them up it seemed fine so I won't bother re-recording like I had mentioned. I hope it helps anyone who wants to test their relay to see if it reacts the same.
Had a few minutes so I tried this.
Quote: The relay can be tested out of circuit by grounding both the housing bracket and the terminal that the blue-yellow wire would normally connect to. Then apply 12V to the terminal where the yellow-green wire usually connects. With your meter touching the relay housing and the terminal that the black wire typically connects to, you should see a 12V reading. (I got 0 volts.)
Quote: If the battery is hooked up normally and you can seat the relay connector enough to establish contact with the yellow-green and black wires, then grounding the terminal that the blue-yellow wire normally connects to should cause the horn to sound. (The horn did not sound)
Sounds like the relay is bad. I like the LITTLEFUSE relays from Ford which is what I was testing in my video.
C4AZ-13853-A - RELAY and BRACKET ASSY. HORN
There are a few on eBay right now. They will have LITTLEFUSE stamped on the housing. Great old brand. As with anything of that age even if new in the box there is a chance someone tried it and it didn't seem to work so they put it back in the box but hopefully that bug doesn't bite you. One for $38.71 and $5.15 shipping - that is not a bad deal. Almost any electrical switch in new working order is worth $75 these days - and no tariffs!!
First off, Thank You to all who helped for your patience and replies. Victory is mine. I now have a working horn , after replacing the horn relay. Beep Beep. I just ran up to the local Oreilly Auto Parts and picked one up. I should have probably done it sooner, i thought I had that part sorted out. I was wrong. No regrets though, it was a great learning experience. I have a much better understanding of how the horn circuit works. Thanks again.
Last edited by 66Classic96; Oct 16, 2025 at 05:45 PM.
First off, Thank You to all who helped for your patience and replies. Victory is mine. I now have a working horn , after replacing the horn relay. Beep Beep. I just ran up to the local Oreilly Auto Parts and picked one up. I should have probably done it sooner, i thought I had that part sorted out. I was wrong. No regrets though, it was a great learning experience. I have a much better understanding of how the horn circuit works. Thanks again.
The Sweet Sweet sound of success!
I needed a copper brush for a non vehicle project one time. Couldn’t find the correct part, so I made one out of a MiG welder tip. I think it was for .025 wire. Easy to find, cheap, and it worked just fine. Soldered in a wire, filed it square, got things going again.
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I now have a working horn , after replacing the horn relay. Beep Beep. I just ran up to the local Oreilly Auto Parts and picked one up. I should have probably done it sooner, i thought I had that part sorted out. I was wrong. No regrets though, it was a great learning experience. I have a much better understanding of how the horn circuit works. Thanks again.
